Silicon nanowires grown inside nitrogen-doped hollow carbon spheres as anode materials for lithium-ion batteries

Abstract

Silicon has the highest theoretical lithium storage capacity, low discharge potential, abundance in the earth's crust and environment-friendly nature, which has been considered as one of the most promising anode materials for lithium-ion batteries. However, high-cost raw materials, complicated processes and harsh reaction conditions are generally used in the preparation of silicon. In addition, the poor intrinsic conductivity, slow diffusion kinetics of lithium-ion and large volume expansion in silicon hinder its further application. Here, Si nanowires@nitrogen-doped hollow carbon spheres (Si NWs@N-HCSs) as anode materials for lithium-ion batteries are prepared by the polystyrene template method, sodium citrate as the reducing agent, high-temperature carbonization of polypyrrole, and the “supercritical fluid-liquid-solid (SFLS)” growth mechanism. The initial Coulombic efficiency of as-obtained Si NWs@N-HCSs is 72% at a current density of 0.5 A g-1, and it gives a reversible specific capacity of 568 mAh g-1 after 200 cycles and outstanding rate performance (2709, 2359, 1839, 1566, 1421, and 1028 mAh g-1 at 0.2, 0.5, 1, 2, 4, and 8 A g-1). The excellent electrochemical behavior of the composite electrode is attributed to the nitrogen-doped carbon spheres with hollow structure, gold nanoparticles with high conductivity, and silicon with nanowire structure. This study not only provides a new synthetic idea for the application of silicon in other fields, but also offers a new design strategy for the improvement of lithium storage properties of silicon-based anode materials.