Activated natural porous silicate for a highly promising SiOx nanostructure finely impregnated with carbon nanofibers as a high performance anode material for lithium-ion batteries

Abstract

A highly promising anode material with an amorphous SiO_x nanostructure finely impregnated with carbon nanofibers is presented. The nanostructure material has a unique integral feature in that carbon nanofibers smaller than several nm in diameter are finely dispersed in amorphous SiO_x media in an aligned manner. The synthetic route to fabricate the nanostructure is very simple and easy, using natural porous silicate, sepiolite, activated through the process of sintering and acid treatments on carbon source-loaded sepiolite nanocomposites. Upon the treatments, the nanocomposite material is changed in respect of its structure and chemical composition from crystalline Mg silicate to the carbon nanofiber-impregnated amorphous SiO_x phase (CNF–SiO_x nanostructure), and the electrochemical activity is greatly improved. The CNF–SiO_x nanostructure exhibits excellent electrochemical performance with a reasonably high capacity of approximately 720 mA h g⁻¹ for a current density of 70 mA g⁻¹ (C/10 rate) and outstanding rate capability with a capacity retention of 96.8% for a current density of 700 mA g⁻¹ and 87% at 1400 mA g⁻¹ relative to that at 35 mA g⁻¹, even at a high electrode loading level above 8 mg cm⁻². The cycling performance is also very stable, with a capacity retention of 94.7% over 50 cycles at a rate of 350 mA g⁻¹ and with a Coulombic efficiency above 99%.