A low-temperature ionic liquid system for topochemical synthesis of Si nanospheres for high-performance lithium-ion batteries†

Abstract

Silicon is utilized as a functional material in various fields such as semiconductors, bio-medicine, and solar energy. To prepare Si materials, researchers have proposed methods including carbothermal reduction, hydrothermal reduction, and magnesiothermal reduction, but these strategies often involve high temperatures or unwanted by-products. Herein, we present a low-temperature ionic liquid reduction system to prepare Si nanospheres based on 1-butyl-3-methylimidazolium chloride-aluminum chloride ([Bmim]Cl-AlCl₃). In this low-temperature solution system, AlCl₃ not only absorbs the heat generated in the reaction, but also can be reduced by metallic Mg to active intermediates, which participate in the reduction of SiO₂. Furthermore, spherical SiO₂ can be gently reduced to spherical nano-Si with preserved morphology in the [Bmim]Cl-AlCl₃ system. When the prepared Si nanosphere electrode is employed as the anode in lithium-ion batteries, it demonstrates an initial coulombic efficiency of 82.9% and a capacity retention of 94.2% after 100 cycles at 0.5 A g⁻¹. Moreover, the SVC electrode, obtained by reducing SiO₂@C, exhibits almost no capacity decay after 100 cycles and retains a specific capacity of 914 mA h g⁻¹ after 600 cycles at 2 A g⁻¹. This study provides an alternative, mild preparative route to Si-based functional materials with preserved morphology and components of the Si precursors.