Tuning Si@SiO_x core/shell structures by controlling the microwave heating temperature for ultrafast lithium-ion battery anodes

Silicon is a promising anode material for lithium-ion batteries (LIBs) owing to its high specific capacity (∼3590 mAh/g). To achieve high-performance Si-based anodes, the large volume expansion of Si particles during lithiation and delithiation is a critical problem to resolve. Herein, a core/shell structure is proposed for silicon suboxide (SiO_x) coated on a Si surface using microwave and magnesiothermic reduction processes. We controlled the optimized Si@SiO_x amorphous shell thickness by adjusting the microwave temperatures to 50, 150, and 250 °C. The Si@SiO_x core/shell structure with the optimal oxide layer thickness exhibited a high capacity (630.178 mAh/g at 1000 mA/g), a notably improved initial coulombic efficiency (77.49 %), excellent cycling performance (70.08 % capacity retention up to 200 cycles), and significantly decreased swelling. The enhanced electrochemical performance was mainly attributed to the Si@SiO_x core/shell structure with an optimal oxide layer thickness on the surface as well as interfacial resistance, lithium-ion diffusion rate, oxygen vacancies, and porous morphology optimized by the Si@SiO_x core/shell structure. This study provides a facile avenue for the surface engineering of Si nanoparticles for high-performance Si anodes of LIBs.