Study On Electrodeposition Of Silicon From Silicon Industry By-product Silicon Tetrachloride In Ionic Liquids

With the acceleration of industrialization,the shortage of non-renewable energy,Greenhouse Effect,environmental pollution and other problems are becoming more and more serious.In the world energy structure,green and renewable solar energy will occupy more and more important seats,replace part of non-renewable fossil energy,and become the main body of energy supply.The development of solar photovoltaic industry promotes the rapid development of polysilicon industry.It is inevitable that silicon tetrachloride,a by-product of silicon tetrachloride,will be produced in the production of polysilicon industry.Silicon tetrachloride is a kind of strongly corrosive,toxic and harmful liquid,which will seriously pollute the environment if it is not properly treated.Therefore,it is necessary to recycle the crystalline silicon by-product silicon tetrachloride.The preparation of silicon by electrochemical deposition of SiCl₄,dissolved in ionic liquid was studied.The suitable ionic liquids were selected by measuring the solubility and conductivity of different ionic liquids,and the dissolution of SiCl4 dissolved by ionic liquids was simulated and verified by COSMO-RS method.The target ionic liquid[N₁₁₁₄][TNf₂]was prepared by direct synthesis.The structure of[N₁₁₁₄][TNf₂]was characterized by Raman spectroscopy.The connection mode between[N₁₁₁₄][TNf₂]and SiCl₄ was studied by infrared spectroscopy.The results show that[N₁₁₁₄][TNf₂]and SiCl₄ are connected by Si-O bond,Si-C bond and C-Cl bond.When the cationic alkyl chain length is Ding Ji,the solubility of quaternary ammonium ionic liquids to SiCl₄ is higher than that of imidazole ionic liquids,The dissolution effect of different anions on SiCl₄ is[TNf₂]>PF₆>BF₄;under the same conditions,the solubility of quaternary ammonium ionic liquids increased with the increase of alkyl main chain length and decreased with the increase of alkyl side chain length.The electrodeposition system of[N₁₁₁₄][TNf₂]-SiCl₄ in argon filled vacuum glove box was studied.Titanium plate was used as working electrode,Pt plate to electrode and silver electrode as quasi-reference electrode.The effects of SiCl₄ concentration,electrolysis temperature and current density on current efficiency,energy consumption and surface morphology of the deposit were studied experimentally.The results show that the deposition effect is the best when the concentration of SiCl₄ is 0.35 mol/L,the electrodeposition temperature is 30?and the current density is 30A/m².The deposited silicon layer is characterized by EDS,XRD and Raman spectra.The results show that the deposited layer is dense and uniform spherical amorphous silicon.The by-product silicon tetrachloride in the actual polysilicon industry was analyzed by ICP-OES.The results show that the main impurity ions in the actual polysilicon by-product SiCl4 are Al,B,Fe,Ti and Zn.The doping electrolyte was tested by cyclic voltammetry.The results showed that the doping of Al,B,Ti impurity ions had little effect on the reduction potential and electrochemical stability of the electrolyte,and Fe and Zn had a great influence on the stability of the electrodeposition system.The effect of electrolyte cycle times on the current efficiency and energy consumption of electrodeposition was studied.the results showed that the current efficiency decreased and the energy consumption increased with the increase of electrolyte cycle times.The infrared characterization of the ionic liquid before and after electrodeposition showed that the peak position of the infrared spectrum of the ionic liquid did not change obviously,the intensity of the absorption peak decreased to a certain extent,and the structure of the electrolyte changed obviously.The recycling of electrolyte is feasible.