Crystallinity-controlled SiO_x anode material prepared through a salt-assisted magnesiothermic reduction for lithium-ion batteries

Silicon suboxides (SiO_x) are considered potential anode materials for high-energy lithium-ion batteries (LIBs) owing to their high specific capacity and stable cycling performance. Several structural parameters, such as chemical composition, particle size, surface area, and crystallinity, affect the electrochemical performance of SiO_x. In particular, the crystallinity of the Si embedded in the SiO₂ matrix significantly influences the electrochemical performance of SiO_x, as it directly affects the structural stability of Si during cycling. To optimize the high-performance synthesis of SiO_x, we conduct a comparative study of the heat absorbents (KCl and NaCl) to demonstrate their critical role in determining the crystallinity of SiO_x particles during the magnesiothermic reduction of SiO. The different heat capacities of these absorbents induced distinctive structural evolutions of SiO during the process, affecting the electrochemical behavior of SiO_x during cycling. When KCl was present, the resulted substance has a lower crystallinity of Si, thereby offering superior electrochemical performance compared to that in the presence of NaCl. KCl-SiO_x exhibited a high reversible capacity of 1862 mAh g⁻¹ and an initial Coulomb efficiency (ICE) of 83.0%. Moreover, a stable cycle performance of up to 200 cycles and high capacity retention of up to 89.1% at a current density of 750 mA g⁻¹ could be achieved. Therefore, we believe that the results obtained herein will provide a basis for the development of high-performance SiO_x anode materials for commercial applications.