Optimizing the function of SiOx in the porous Si/SiOx network via a controllable magnesiothermic reduction for enhanced lithium storage

Highlights: • The distribution and relative content of SiO_x were regulated in Si/SiO_x network. • Residual SiO_x randomly embedded within network has a positive effect on stability. • SiO_x core accelerates the broken of particles obtained from incomplete reduction. -- Abstract: Silicon anodes hold promise to be a possible candidate to replace graphitic carbon used in practical applications. However, it undergoes a huge volume change in the process of electrochemical alloying, which leads to electrical isolation in the long-term cycle. In this work, we focus on regulating the thermal reduction reaction to change the distribution and relative content of residual SiO_x in the network of active materials. By analyzing the structure and composition of the product under different reaction conditions combined with electrochemical performances, it is confirmed that there is still a small amount of residual SiO_x embedded in the reduced silicon nanoparticles for the completely reduced products which have a positive effect on the cycle stability, while the SiO_x core accelerates the particle breakage under the incomplete reduction condition, which is further confirmed by micrograph of the electrode after cycling. Specifically, 628 mAh g⁻¹ of specific capacity can be retained after 100 cycles for almost pure silicon products reduced by 8 h at 660 °C, which is better than commercial nanometer silicon anodes. This work provides a theoretical guidance for the construction of silicon anode by thermal reduction, and is conducive to the expansion of this method for the synthesis of practical silicon matrix.