In Situ Pyrolysis Concerted Formation Of Silicon-Based Composites During Molten Salt Electrolysis Of Silicon-Containing Compound

Silicon-containing biomass is a potential precursor of carbon-based and silicon-based materials,which contains abundant organic components and inorganic SiO₂.However,during the preparation of carbon-based materials,SiO₂ and other impurities are removed by acid or alkali solvent extraction.In the preparation of silicon-based materials,organic components are removed through combustion and other impurity elements are removed by acid soaking.Currently,there are some drawbacks including the use of additional reagents,complex operation process,low efficiency and inability to utilize Si and C elements in biomas simultaneously.To achieve high efficiency,short-process utilization and high value-added product of silicon-containing biomass,experiments are carried out on molten-salt assisted electro-chemical conversion of typically silicon-containing biomass(rice husks)based on the simultaneous utilization of Si and C elements in biomass.Initially,SiO₂@polydopamine(SiO₂@PDA)is used as a simulator of rice husks(RHs)to investigate its electrochemical behavior in molten salt for obtaining the best treatment condition for biomass.The main contents of this thesis are as follows:(1)Si/C hybrids(named Si@C@Si)are obtained by a one-pot electrochemical treatment via pyrolysis-cum-electrolysis(PCE)of SiO₂@polydopamine(SiO₂@PDA)in molten Ca Cl₂-Na Cl at 800°C.The obtained hybrids are composed of outmost silicon thin layers due to electrodeposition,sandwiched N-doped carbon hollow spheres derived from pyrolysis of PDA,and encapsulated silicon nanoparticles stemming from direct electrodeoxidation of SiO₂.The PCE protocol shows intriguing merits on accelerated electroreduction of SiO₂ and retarded generation of inconvenient Si C.The preparation conditions of Si@C@Si are optimized by varying electrolysis time and applied voltage,with the optimal conditions being identified as PCE at 2.6 V for 2 h.When evaluated as an anode for lithium-ion batteries,the obtained Si@C@Si exhibites a reversible specific capacity of 904 m Ah g^-1 after 100galvanostatic charge/discharge cycles at 500 m A g^-1.The proposed PCE method is highlighted as an intensified Si extraction method for advanced lithium-ion batteries,promising practical applications.(2)Based on the optimal conditions of treatment of SiO₂@PDA,Si C/C composite is realized via a molten salt-assisted electrochemical method.In order to obtain the single Si material,the weight ratio between SiO₂ and organic matter is adjusted by the addition of SiO₂.The results show that the content of Si C in RHs-derived product is greatly reduced and Si becomes the main component.