A Low-temperature Ionic Liquid System to Topochemically Synthesize 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 room-temperature ionic liquid reduction system to prepare Si nanospheres based on 1-butyl-3-methylimidazolium chloride-aluminum chloride ([Bmim]Cl-AlCl3). In this room-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 participates in the reduction of the 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 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.