As current electronic devices need more capacity and long-lived energy storage, new materials that possess more energy storage are of highly desirable. Silicon presents capacity of 3580 mAh/g as anode material for lithium-ion batteries (LIBs), of which capacity is much higher than the capacity (372 mAh/g) of current graphite anode; thus it has been believed as a next-generation anode material for LIBs. Silicon anode suffers from several technical issues, however, which are of severe volume change up to 400 % during cycling and low electric conductivity. In addition, at the first cycle, silicon reacts excessively with the electrolyte to generate solid-electrolyte interface layer (SEI layer) due to volume expansion, which reduce the coulombic efficiency (CE), eventually resulting in lower the capacity of the battery. In order to compensate theses disadvantages, the Si@C yolk-shell structure has been designed via various ways, among which magnesiothermic reduction of SiO<sub>2</sub>@C composite to prepare Si@C yolk-shell structure has been of great interest in.<br/>Herein, we first report that complete pore blockage and local graphitization of carbon shell were identified during magnesiothermic reduction, which has not been reported so far. The microposority of carbon shell was completely blocked after magnesiothermic reduction, determined by nitrogen sorption measurement. In addition, local graphitization of carbon shell was observed under TEM analysis and Raman analysis also supported the increase of graphitization degree. Such unexpected finding could be ascribed to the exothermic reduction nature of magnesiothermic reduction, resulted in graphitization and consequent pore blockage of carbon. As prepared Si@C yolk-shell structure exhibited outstanding capacitance of 1500 mAhg-1 (@100 cycles) with stable long term stability and prominent rate performance.

Unexpected finding of pore blockage & local graphitization of Si@C yolk-shell structure during magnesiothermic reduction

256th National Meeting (2018)

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