Highly–stable Ternary Si/Carbon Nanotube/Carbon Nanofiber Anodes for Li-Ion Batteries

Abstract

Despite the highest theoretical capacity, silicon anodes for Li-ion batteries have two critical drawbacks of (i) severe volume expansion leading to electrical disconnection and (ii) formation of poor electronic conductive solid–electrolyte interface caused by deformation of electrolyte at low potential,[1,2 ] leading to a poor cycle performance. Herein, we fabricated ternary silicon nanoparticles (Si NPs) /carbon nanotube (CNTs) /carbon nanofibers (CNFs) via water-based electrospinning process, followed by carbonization. Since CNTs provide excellent electrical and electronic properties from their one–dimensional (1–D) feature, they could be easily assembled with Si NPs into nanofibers and improve the charge conductivity and structural stability for our anodes. Furthermore, the carbon nanofibers made from polyvinyl alcohol polymer can make Si NPs connected each other to form networking electrodes. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests of this ternary anode demonstrated better activity and smaller charge transport resistance than pure SiNPs and our previous Si rich carbon nanofibers[3]. Furthermore, more than two-fold increase in the capacity retention was achieved for the ternary anode compared to that of Si rich carbon nanofibers after 100 cycles. In addition, our ternary anodes exhibited about 1,000 mAh/g even at high charging rates after 150 cycles. This improvement of cycle life should be attributed to facilitating charge transport and distribution of Si NPs by employing 1–D CNTs and carbon nanofibrous networks, and our ternary SiNPs/CNTs/CNFs system provided by scalable water-based spinning should overcome current barriers to commercializing Si-based anodes such as pulverization and low production rate.