Electroreduction of Silicon from the NaI-KI-K2SiF6 Melt for Lithium-Ion Power published by Ural Federal University eISSN2411-1414; chimicatechnoacta.ru ARTICLE 2022, vol. 9(4), No. 20229424 DOI: 10.15826/chimtech.2022.9.4.24 1 of 6 Electroreduction of silicon from the NaI–KI–K2SiF6 melt for lithium-ion power sources Rayana K. Abdurakhimova ab *, Michail V. Laptev b , Natalia M. Leonova a , Anastasia M. Leonova a , Alexander S. Schmygalev ab , Andrey V. Suzdaltsev ab a: Institute of Hydrogen Energy, Ural Federal University, Ekaterinburg 620075, Russia b: Institute of High-Temperature Electrochemistry UB RAS, Ekaterinburg 620137, Russia * Corresponding author: arianaboimuradova@yandex.ru This paper belongs to a Regular Issue. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract Silicon and silicon-based materials are increasingly used in microelec- tronics, 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 ad- dition, 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 af- ter their separation from the electrolytes by the ICP, SEM-EDX, XRD and Raman spectroscopy methods. Fiber and thread-like silicon sam- ples 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%. Keywords silicon nanofibers electroreduction melt lithium-ion power source cycling Received: 21.10.22 Revised: 01.12.22 Accepted: 01.12.22 Available online: 06.12.22 Key findings ● The possibility of electrodeposition of silicon deposits with a developed surface from the NaI–KI–K2SiF6 melt at a temperature from 650 to 750 °С was shown for the first time. ● The energy characteristics of the obtained silicon in the anode material of a lithium-ion current source during cycling were determined. 1. Introduction Silicon and silicon-based materials are becoming widely used in microelectronics, metallurgy and power generation [1]. Silicon materials to be used in devices for solar energy conversion, accumulation and storage are being actively de- veloped [2–4]. Silicon is a promising anode material for lithium-ion power sources because its specific lithium-ad- sorption capacity (4200 mAh·g–1) is by an order of magni- tude higher than those of graphite-containing anode mate- rials (372 mAh·g–1) [5–7]. However, high silicon anode lith- ium-adsorption capacity implies a significant volume ex- pansion (up to 300%) that may result either in destruction of the power source or in the contact fault between the an- ode material and the substrate (current collector). Application of composite materials based on nano-size or submicron silicon particles is one of the possible ways to solve this problem [8, 9]. The methods of carbothermal reduction of quartz fol- lowed by refining the obtained silicon from admixtures via chlorination and hydration [10] were implemented in the industrial scale, but thus-obtained silicon has a form of crystals of several tens of µm is size. To obtain nano-size silicon crystals, relatively complex and expensive methods of laser ablation, plasma chemical synthesis, laser-induced dissociation, etc. [11], are known. These methods are un- suitable for industrial silicon production. Methods of silicon electroreduction from molten salts for producing the nano- and micro-sized silicon with http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.4.24 mailto:arianaboimuradova@yandex.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-3338-0057 https://orcid.org/0000-0003-1016-8977 https://orcid.org/0000-0001-5900-7045 https://orcid.org/0000-0001-9783-309X https://orcid.org/0000-0003-3004-7611 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.4.24&domain=pdf&date_stamp=2022-12-06 Chimica Techno Acta 2022, vol. 9(4), No. 20229424 ARTICLE 2 of 6 controlled morphology are industrially promising, rela- tively simple and inexpensive. Fluoride mixtures of KF–NaF–LiF, LiF–NaF, LiF–CaF2 and similar compositions were suggested as first possible electrolytes for silicon production at the process tempera- tures ranging from 500 to 1500 °С [12–14]. However, their main drawback was the difficulty of separating the fluoride residues from the cathode deposits because of their low sol- ubility in water and high boiling temperatures. High chem- ical aggressiveness to the reactor materials is the main dis- advantage of fluoride melts, which limits the possible range of their application and leads to the complication of the re- actor construction as well as to the silicon contamination by the corrosion products. The KCl–KF system with KF concentration up to 66 mol.% was suggested as a water-soluble electrolyte that is a good solvent for both K2SiF6 and SiO2 [15–17]. A relative aggressiveness of KF to the reactor materials and a required decontamination of KF from H2O and HF during the molten KCl–KF mixture preparation are the disadvantages of the method of electrolytic silicon production. All mentioned factors may cause the melt composition instability and ap- pearance of the admixtures in the obtained silicon. Molten electrolytes based on CaCl2–CaO, where SiO2 is a source of silicon, were extensively studied for the electro- lytic silicon production [18–20]. The advantages of these electrolytes include high CaCl2 solubility in water that al- lows separating deposits from the electrolyte residues after the electrolysis and lower chemical aggressiveness, as com- pared with fluorite salts, to the reactor materials. Among the disadvantages of this method, we should mention a rel- atively high temperature, unstable composition of electro- active ions in the molten electrolyte and presence of oxide admixtures, which causes inevitable appearance of oxygen in the silicon deposit bulk. To decrease the electrolysis temperature, stabilize the composition of the silicon-containing electroactive parti- cles and to control the morphology of silicon deposits, the melts containing iodides may be used. In particular, the KCl–KF–KI–K2SiF6 system containing KI up to 75 mol.% [21] is assumed to eliminate the presence of water traces in the reactor and, therefore, the requirements to the preparation of the molten electrolytes and equipment used increase. Electrodeposition of silicon and silicon-based materials from low-temperature ionic liquids and organic electrolytes is also a promising direction [22–26]. However, the produc- tivity of such methods seems to be relatively low, and the organization of feeding the electrolyzer with SiCl4 is more complex and requires additional equipment. In this work, we studied the possibility of electrodepo- sition of fibrous silicon deposits from the NaI-KI-K2SiF6 melt as well as the cycle ability of the obtained silicon de- posits in the lithium-ion current sources with silicon-based anodes. The selected melt is promising for silicon electrodep- osition, since it has a relatively wide range of compositions with a liquidus temperature below 700 °C [27]. 2. Experimental 2.1. Electrolyte preparation Electrolytes for silicon electroreduction were prepared in a glassy carbon crucible from commercial chemically pure in- dividual NaI and KI salts (Reakhim, Russia) and commercial reagent grade K2SiF6 (Reakhim, Russia), which was prelim- inary subjected to hydrofluoration by stepwise heating to 450 °С in the mixture with NH4F [28]. The salt mixture of (wt.%) 56NaI–44KI was purified from oxygen and other ad- mixtures immediately prior to the experiments. The salts were mixed with elemental iodine, heated stepwise to 400 °С and exposed for 3–4 h. The evaporating iodine in- teracted with oxides according to reaction (1) [21]: 2M2O + I2 = 4MI + O2 (M = K, Na) (1) After this, the mixture was heated to the working tem- perature, and the obtained melt was additionally subjected to the galvanostatic electrolysis at the cathode current den- sity of 0.02 A·cm–2 during 2–4 h. A graphite cathode and an insoluble glassy-carbon anode (crucible) were used. The electrolysis durability was determined empirically by the moment of shifting the electrode potential to the potential of alkali metal electroreduction. During the electrolysis, electropositive admixtures (Fe, Ni and etc.) were depos- ited on the cathode and removed from the reactor with a cathode. 2.2. Reactor for the silicon synthesis The experiments on the silicon electroreduction were per- formed at the temperatures from 650 to 750 °С in a her- metically sealed quartz reactor with the pure argon atmos- phere. A glassy carbon container with a molten electrolyte was located at the bottom of the reactor. The walls of the reactor were screened with nickel foil to protect them from possible salt vapors. The electrodes and the control thermo- couple were assembled to the fluoroplastic cover of the re- actor. Cylindrical graphite bars of the MPG8 grade (Tech- noCarb company, Chelyabinsk, Russia) were preliminary rinsed in acidic water solution and dried under vacuum. There bars served as working electrodes. Monocrystalline silicon (99.9999 wt.%) was used as a counter electrode and a quasi-reference electrode. The silicon electroreduction from the NaI-KI melt with the addition of 7 wt.% of K2SiF6 was performed under the potentiostatic regime at the cathode overpotential of 0.2 V and under galvanostatic regime at the cathode current density ranging from 1 to 5 mA·cm–2. The parameters of the electrolysis were determined during the process of sil- icon electroreduction in halide melts in the temperature range of 700–750 °С [15–17, 29]. The electrolysis was per- formed using a PGSTAT AutoLAB device with the Nova 1.12 software (Metrohm, Netherlands). When the electrolysis was terminated, the deposits were lifted from the melt, cooled down to room temperature and then removed from the reactor. Chimica Techno Acta 2022, vol. 9(4), No. 20229424 ARTICLE 3 of 6 The electrolyte residues were removed from the depos- its by the high-temperature distillation under the argon flow at 950 °С for 6–8 h. During this procedure, cathode sediments with the salt residues were heated in argon to a temperature of 950 °C. In these conditions, the component with the highest vapor pressure (salts) evaporated and crystallized in the cold part of the distillation device [30]. The conventional method (washing out electrolyte residues in water-acid solutions) is less effective in the case of fi- brous deposits, since it leads to silicon oxidation and its sig- nificant losses. 2.3. Analysis of the melts and deposits The concentration of silicon in the melt before and after the electrochemical measurements and electrolysis was deter- mined using the atomic-emission method by an iCAP 6300 Duo spectrometer (Thermo Scientific, USA). The morphology of the obtained deposits was studied using a scanning electron mi- croscope Tescan Vega 4 (Tescan, Czech Republic) with an Xplore 30 EDS attachment (Oxford, Great Britain). The phase composition and the presence of Si–Si and Si–O bounds were determined by the XRD and Raman spectroscopy methods us- ing a “Leica DMLM” microscope and “Renishaw U1000” spec- troscope (Great Britain) equipped with a notch-filter and CCD camera (solid state laser produced by Cobolt Samba company (Sweden) of the 50 mW capacity). 2.4. Electrochemical characteristics of silicon The electrochemical characteristics of the obtained silicon powders at lithiation/delithiation were tested in the com- position of the composite anode of the lithium-ion power source containing (wt.%): 80 – silicon, 10 – carbon, 10 – bounding polyvinylidene difluoride dissolved in N-methyl- 2-pyrollidone. The samples of lithium-ion power sources were assembled in a hermetically sealed argon box with the concentration of admixtures (O2, H2O) not exceeding 0.1 ppm. The anode material was spreaded on the steel net, a lithium foil served both as a counter electrode and as a reference electrode. All electrodes were separated from each other by two separator layers. A solution of LiPF6 in the mixture of ethylene carbonate/dimethyl carbonate/di- ethyl carbonate was used as the electrolyte. The purity of all elements used was 99.99 wt.% (Sigma-Aldrich, Ger- many). The measurements were performed by the gal- vanostatic cycling using a multichannel potentiostat Wonatech WBCS-3000 M2 (WonATech Co., Ltd., Korea). 3. Results ana Discussion 3.1. Silicon electroreduction The parameters and results of the silicon electroreduction are illustrated in Table 1. Depending on temperature, elec- trolysis regime and parameters, fiber and thread-like sili- con deposits of 50 to 320 nm in diameter and up 20 µm in length were primarily obtained on the graphite cathode. The microphotographs of the typical deposits are presented in Figures 1 and 2. According to the EDS analysis, the concentration of admixtures in the obtained silicon varied from 1.2 to 4.6 wt.%. Oxygen was the main admixture. We have not been able yet to determine whether it is a surface oxide or a bulk one. However, we assume that this is surface oxygen and oxidated Si, since the methods and devices used allow the electrodeposition to be carried out as cleanly as pos- sible. Figures 3 and 4 provide the X-ray diffraction pattern and Raman spectra of the obtained silicon deposit. It is seen that the sample has the form of polycrystalline silicon with SiO2 ad- mixtures. Only a Si–Si bond is observed, which testifies that there is no interaction between the deposited silicon and the carbon substrate under the experiment conditions. 3.2. Electrochemical characteristics of silicon Figure 5 provides potential dependencies of Si/C composite anodes, fabricated from the fiber (sample 1) and thread-like (sample 2) silicon deposits, in the composition of the exper- imental lithium-ion power sources, during their first lithi- ation/delithiation cycle (forming cycling). It is seen that the anode is subjected to charging and discharging, which proves the possibility of application of such anodes in lith- ium-ion power sources. Table 1 Parameters and results of silicon electroreduction from the NaI-KI melt with addition of 7 wt.% of K2SiF6. No. t, °C i, mA cm–2 Over- potential, V Time, min Deposit 1 650 1 – 60 Fibers, Ø 60–160 nm 2 700 – 0.2 40 Threads, Ø 130–200 nm 3 750 5 – 25 Fibers, Ø 90–320 nm Figure 1 Microphotographs of a typical fiber silicon deposit ob- tained by the electrolysis of the NaI-KI-K2SiF6 melt at a cathode current density of 5 mA cm–2 and 750 °C before (a) and after (b) the electrolyte residues removal. Chimica Techno Acta 2022, vol. 9(4), No. 20229424 ARTICLE 4 of 6 Figure 2 Microphotographs of a typical thread-like silicon deposit obtained by the electrolysis of the NaI–KI–K2SiF6 melt at 700 °C and cathode overpotential of 0.2 V after the electrolyte residues removal. Figure 3 X-ray diffraction of the silicon deposit, obtained by the electrolysis of the NaI–KI–K2SiF6 melt at a cathode current density of 5 mA cm–2 and 750 °C after the electrolyte residues removal. Figure 4 Raman spectra of the silicon deposit, obtained by the elec- trolysis of the NaI–KI–K2SiF6 melt at a cathode current density of 5 mA cm–2 and 750 °C after the electrolyte residues removal. The inclined regions at the potentials of 0.2–1.25 V for the sample 2 and at the potentials of 0.2 and 1.2 V for the sam- ple 1 correspond to the process of electrode/electrolyte in- terphase boundary formation (SEI). On the charge curves (left part) there is a region where the potential stabilizes at 0.18 V. The characteristic plateau in the region of 0.1-0.2 V corresponds to the process of lithium intercalation into sil- icon according to reaction [31]: Siy + xLi+ xe →LixSiy. (2) The discharge (right part) curves illustrate an abrupt potential jump up to 1.4 V, which corresponds to the pro- cess of silicon deintercalation. During the first (forming) cycling the coulombic efficiency of the charge/discharge process was 60%. To estimate the reversibility of the anode material, CVs of samples 1 and 2 were also obtained after its cycling (see Figure 6). From them, we can draw a preliminary conclu- sion about the presence of reversibility (the presence of peaks in the cathode and anode regions) of the samples, as well as the closeness of the lithium reduction/oxidation po- tentials to the charge/discharge potentials from the de- pendences shown in Figure 5. To determine the discharge capacity and coulombic effi- ciency (the ratio of the charge capacity to the discharge one) a galvanostatic cycling of the experimentally obtained samples was charged at the current of 200 mA·g–1. We per- formed 30 cycles. Figure 7 presents the dependencies of dis- charge capacity and coulombic efficiency of the samples during cycling. After 30 charge/discharge cycles, the dis- charge capacity of the anode samples composed of fiber and thread-like silicon decreased from 1390 and 1610 to 440 and 565 mAh·g–1, and the coulombic efficiency was 89 and 91%, respectively. An irreversible capacity may be ex- plained by the presence of SiO2 admixture that transforms into lithium silicate during the lithiation, by the interaction of the substrate components with silicon and lithium, and by the destruction of silicon fibers and the contact fault with the substrate [32]. Further research is needed to de- termine the reasons for such behavior. Figure 5 First charge/discharge cycle of half-elements with sili- con-based composite anodes. 0 10 20 30 40 50 60 70 80 2Theta / In te n si ty / c p s 1 - Si 2 - SiO2 1 1 1 1 12 98.4 1.5 Si SiO2 0 100 200 300 400 500 600 700 800 900 Raman shift / cm-1 In te n si ty 510 cm-1 Si-Si bond 0.0 0.4 0.8 1.2 1.6 0 10 20 30 40 50 60 70 80 90 Е (v s E L i/ L i+ ), V time, h sample 1 sample 2 Chimica Techno Acta 2022, vol. 9(4), No. 20229424 ARTICLE 5 of 6 Figure 6 CVs for samples of silicon-based composite anodes after cycling. Sweep rate of 0.1 mV s–1. Figure 7 Change in the discharge capacity and coloumbic efficiency of the charge/discharge process of the samples during cycling. 4. Conclusions The possibility of using silicon fibers electrolytically pro- duced from the NaI–KI–K2SiF6 melt at 650–750 °C in com- posite Si/C anodes of lithium-ion power sources was stud- ied. The silicon electroreduction was performed under the galvanostatic regime at the cathode current density ranging from 1 to 5 mA cm–2, as well as under the potentiostatic re- gime and the cathode overpotential of 0.2 V. The electroly- sis was found to result in the formation of fiber and thread- like silicon deposits with the average diameter from 60 to 320 nm and length up to 20 µm. According to the analyses, the concentration of admixtures, primarily oxygen, in the obtained deposits varied from 1.2 to 4.6 wt.%. The energy characteristics of the obtained silicon sam- ples were determined during their lithiation-delithiation in the composition of the lithium-ion power source. After 30 cycles, the discharge capacity of the anode samples of fiber and thread-like silicon decreased from 1390 and 1610 to 440 and 565 mAh·g–1, and the coloumbic efficiency was 89% and 91%, respectively. We assume that the irreversi- ble capacity of the samples may be associated with the pres- ence of SiO2 admixture; it also may be caused by the inter- action of the substrate components with silicon and lithium as well as by the destruction of silicon fibers and contact fault between silicon and the substrate. Supplementary materials No supplementary materials are available. Funding The work was performed within the Agreement No. 075-03- 2022-011 dated 14.01.2022 (theme number FEUZ-2020- 0037). Acknowledgments The facilities of the Composition of Compounds the Shared Access Center of Institute of High-Temperature Electro- chemistry UB RAS were used in this work. Author contributions Conceptualization: A.V.S. Data curation: R.K.A., A.V.S. Formal Analysis: R.K.A., N.M.L., A.M.L. Funding acquisition: A.V.S. Investigation: R.K.A., M.V.L., N.M.L., A.M.L. Methodology: R.K.A., A.S.S., N.M.L., A.M.L. Project administration: A.V.S. Resources: R.K.A., M.V.L., N.M.L., A.M.L. Supervision: A.S.S., A.V.S. Validation: N.M.L., A.M.L., A.V.S. Visualization: R.K.A., A.V.S. Writing – original draft: R.K.A., N.M.L., A.M.L. Writing – review & editing: A.V.S. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: Michail V. Laptev, Scopus ID 57203958198; Natalia M. Leonova, Scopus ID 57352201500; Anastasia M. Leonova, Scopus ID 57352053900; Alexander S. Schmygalev, Scopus ID 56458886600; Andrey V. Suzdaltsev, Scopus ID 55218703800. Websites: Ural Federal University, https://urfu.ru/en; Institute of High-Temperature Electrochemistry, http://www.ihte.uran.ru. References 1. Cohen U. Some prospective applications of silicon electrodep- osition from molten fluorides to solar cell fabrication. J Elec- tron Mater. 1977;6:607–643. doi:10.1007/BF02660341 2. Gevel T, Zhuk S, Leonova N, Leonova A, Trofimov A, Su- zdaltsev A, Zaikov Yu. Electrochemical synthesis of nano- sized silicon from KCl-K2SiF6 melts for powerful lithium-ion batteries. Appl Sci. 2021;11(22):10927. doi:10.3390/app112210927 -1.2 -0.8 -0.4 0 0.4 0.8 0 0.2 0.4 0.6 0.8 1 sample 1 sample 2 I, m A E (vs ELi/Li+), V 0.5 0.6 0.7 0.8 0.9 1.0 400 800 1200 1600 0 10 20 30 C o lo u m b ic e ffic ie n c y D is c h a rg e c a p a c it y, m A h g -1 Cycles sample 1 sample 2 https://www.scopus.com/authid/detail.uri?authorId=57203958198 https://www.scopus.com/authid/detail.uri?authorId=57352201500 https://www.scopus.com/authid/detail.uri?authorId=57352053900 https://www.scopus.com/authid/detail.uri?authorId=56458886600 https://www.scopus.com/authid/detail.uri?authorId=55218703800 https://urfu.ru/en http://www.ihte.uran.ru/ https://doi.org/10.1007/BF02660341 https://doi.org/10.3390/app112210927 Chimica Techno Acta 2022, vol. 9(4), No. 20229424 ARTICLE 6 of 6 3. Zh Yu, Fang Sh, Wang N, Shi B, Hu Y, Shi Zh, Shi D, Yang J. In-situ growth of silicon nanowires on graphite by molten salt electrolysis for high performance lithium-ion batteries. Mater Lett. 2020;273:127946. doi:10.1016/j.matlet.2020.127946 4. Islam MM, Said H, Hamzaoui AH, Fukata N, Akimoto K. Study of structural and optical properties of electrodeposited sili- con films on graphite substrates. Nanomater. 2022;12(3):363. doi:10.3390/nano12030363 5. Fang D, Weimin Zh, Haiming Ya, Chengguo S, Geng X, Chen Y, Li L, Liu Z. Surface modification and functional structure space design to improve the cycle stability of silicon based materials as anode of lithium ion batteries. Coat. 2021;11(9):1047. doi:10.3390/coatings11091047 6. Galashev AY, Vorob'ev AS. First principle modeling of a sili- cene anode for lithium ion batteries. Electrochim Acta. 2021;378:138143. doi:10.1016/j.electacta.2021.138143 7. Gevel TA, Zhuk SI, Leonova NM, Leonova AM, Suzdaltsev AV, Zaikov YuP. Electrodeposition of silicon from the KCl–CsCl– K2SiF6 melt. Rus Met (Metally). 2022;2022:958–964. doi:10.1134/S0036029522080237 8. Baranchugov V, Markevich E, Pollak E, Salitra G, Aurbach D. Amorphous silicon thin films as a high capacity anodes for Li- ion batteries in ionic liquid electrolytes. Electrochem Com- mun. 2007;9:796–800. doi:10.1016/j.elecom.2006.11.014 9. Airapetov AA, Vasiliev SV, Kulova TL, Lebedev ME, Metlitskaya AV, Mironenko AA, Nikol’skaya NF, Odinokov VV, Pavlov GYa, Pukhov DE, Rudyi A., Skundin AM. Thin film neg- ative electrode based on silicon composite for lithium-ion batteries. Russ Microelectron. 2016;45:285–291. doi:10.1134/S1063739716030021 10. Wu JJ, Chen Z, Ma W, Dai Y. Thermodynamic estimation of silicon tetrachloride to trichlorosilane by a low temperature hydrogenation technique. Silicon. 2017;9:69–75. doi:10.1007/s12633-015-9353-0 11. Fukata N, Oshima T, Tsuruid T, Ito S, Murakami K. Synthesis of silicon nanowires using laser ablation method and their manipulation by electron beam. Sci Techn Adv Mater. 2005;6:628–632. doi:10.1016/j.stam.2005.06.015 12. Cai Z, Li Y, Tian W. Electrochemical behavior of silicon com- pound in LiF–NaF–KF–Na2SiF6 molten salt. Ionics. 2011;17:821–826. doi:10.1007/s11581-011-0582-y 13. Hu Y, Wang X, Xiao J, Hou J, Jiao Sh, Zhu H. Electrochemical behavior of silicon (IV) ion in BaF2–CaF2–SiO2 melts at 1573 K. J Electrochem Soc. 2013;160:81–84. doi:10.1149/2.035303jes 14. Bieber AL, Massot L, Gibilaro M, Cassayre L, Taxil P, Chame- lot P. Silicon electrodeposition in molten fluorides. Electro- chim Acta. 2012;62:282–289. doi:10.1016/j.electacta.2011.12.039 15. Maeda K, Yasuda K, Nohira T, Hagiwara R, Homma T. Silicon electrodeposition in water-soluble KF-KCl molten salt: Inves- tigations on the reduction of Si(IV) ions. J. Electrochem Soc. 2015;162(9):D444–D448. doi:10.1149/2.0441509jes 16. Zou X, Ji L, Yang X, Lim T, Yu ET, Bard AJ. Electrochemical formation of a p-n junction on thin Film silicon deposited in molten salt. J Amer Chem Soc. 2017;139:16060. doi:10.1021/jacs.7b09090 17. Zhuk SI, Isakov AV, Apisarov AP, Grishenkova OV, Isaev VA, Vovkotrub EG, Zaikov YuP. Electrodeposition of continuous silicon coatings from the KF–KCl–K2SiF6 melts. J. Electrochem. Soc. 2017;164(8):H5135–H5138. doi:10.1149/2.0171708jes 18. Dong Y, Slade T, Stolt MJ, Li L, Girard SN, Mai L, Jin S. Low- temperature molten-salt production of silicon nanowires by the electrochemical reduction of CaSiO3. Angew Chemie. 2017;129:14645–14649. doi:10.1002/anie.201707064 19. Juzeliunas E, Fray DJ. Silicon electrochemistry in molten salts. Chem Reviews. 2020;120:1690. doi:10.1021/acs.chemrev.9b00428 20. Yu Zh, Wang N, Fang Sh, Qi X, Gao Zh, Yang J, Lu Sh. Pilot- plant production of high-performance silicon nanowires by molten salt electrolysis of silic. Ind Eng Chem Res. 2020;59:1–8. doi:10.1021/acs.iecr.9b04430 21. Laptev MV, Isakov AV, Grishenkova OV, Vorob'ev AS, Khu- dorozhkova AO, Akashev LA, Zaikov YuP. Electrodeposition of thin silicon films from the KF-KCl-KI-K2SiF6 melt. J Electro- chem Soc. 2020;167(4):042506. doi:10.1149/1945-7111/ab7aec 22. Hiroki N, Yokoshima T, Momma T, Osaka T. Highly durable SiOC composite anode prepared by electrodeposition for lith- ium secondary batteries. Energy Env Sci. 2012;5(4):6500– 6505. doi:10.1039/C2EE03278C 23. Plugotarenko NK, Myasoedova TN, Grigoryev MN, Mikhailova TS. Electrochemical deposition of silicon-carbon films: A study on the nucleation and growth mechanism. Nanomater. 2019;9:1754. doi:10.3390/nano9121754 24. Tao H, Nara H, Yokoshima T, Momma T, Osaka T. Silicon composite thick film electrodeposited on a nickel micro- nanocones hierarchical structured current collector for lith- ium batteries. J Power Sources. 2013;222:503–509. doi:10.1016/j.jpowsour.2012.09.008 25. Suzdaltsev A. Silicon Electrodeposition for microelectronics and distributed energy: A mini-review. Electrochem. 2022;3:760–768. doi:10.3390/electrochem3040050 26. Xin Q, Hang T, Nara H, Yokoshima T, Li M, Osaka T. Electro- deposited three-dimensional porous Si–O–C/Ni thick film as high performance anode for lithium-ion batteries. J Power Sources. 2014;272:794–799. doi:10.1016/j.jpowsour.2014.09.042 27. Sato T, Toda S, Tachikawa T, Phase diagrams of the Nal-KI and KI-Csl binary systems. Denki Kagaku oyobi Kogyo Butsuri Kagaku. 1987;55(8): 617–620. doi:10.5796/kogyobutsurikagaku.55.617 28. Khudorozhkova AO, Isakov AV, Kataev AA, Redki AA, Zaykov YP. Density of KF–KCl–KI melts. Rus Met (Metally) 2020;2020:918–924. doi:10.1134/S0036029520080078 29. Gevel T, Zhuk S, Suzdaltsev AV, Zaikov YuP. Study into the possibility of silicon electrodeposition from a low-fluoride KCl-K2SiF6 melt. Ionics. 2022;28:3537–3545. doi:10.1007/s11581-022-04573-9 30. Shishkin AV, Shishkin VY, Salyulev AB, Kesikopulos VA, Kholkina AS, Zaikov YP. Electrochemical reduction of ura- nium dioxide in LiCl–Li2O melt. Atomic Energy. 2021;131(2):78–82. doi:10.1007/s10512-022-00850-y 31. Casimir A, Zhang H, Ogoke O, Amine J, Wu G. Silicon-based anodes for lithium-ion batteries: Effectiveness of materials synthesis and electrode preparation. Nano Energy. 2016;27:359–376. doi:10.1016/j.nanoen.2016.07.023 32. Trofimov AA, Leonova AM, Leonova NM, Gevel TA. Electro- deposition of silicon from molten KCl-K2SiF6 for lithium-ion batteries. J Electrochem Soc. 2022;169:020537. doi:10.1149/1945-7111/ac4d6b https://doi.org/10.1016/j.matlet.2020.127946 https://doi.org/10.3390/nano12030363 https://doi.org/10.3390/coatings11091047 https://doi.org/10.1016/j.electacta.2021.138143 https://doi.org/10.1134/S0036029522080237 https://doi.org/10.1016/j.elecom.2006.11.014 https://doi.org/10.1134/S1063739716030021 https://doi.org/10.1007/s12633-015-9353-0 https://doi.org/10.1016/j.stam.2005.06.015 https://doi.org/10.1007/s11581-011-0582-y https://doi.org/10.1149/2.035303jes https://doi.org/10.1016/j.electacta.2011.12.039 https://doi.org/10.1149/2.0441509jes https://doi.org/10.1021/jacs.7b09090 https://doi.org/10.1149/2.0171708jes https://doi.org/10.1002/anie.201707064 https://doi.org/10.1021/acs.chemrev.9b00428 https://doi.org/10.1021/acs.iecr.9b04430 https://doi.org/10.1149/1945-7111/ab7aec https://doi.org/10.1039/C2EE03278C https://doi.org/10.3390/nano9121754 https://doi.org/10.1016/j.jpowsour.2012.09.008 https://doi.org/10.3390/electrochem3040050 https://doi.org/10.1016/j.jpowsour.2014.09.042 https://doi.org/10.5796/kogyobutsurikagaku.55.617 https://doi.org/10.1134/S0036029520080078 https://doi.org/10.1007/s11581-022-04573-9 https://doi.org/10.1007/s10512-022-00850-y https://doi.org/10.1016/j.nanoen.2016.07.023 https://doi.org/10.1149/1945-7111/ac4d6b