Preparation and electrochemical performance of Si@void@NC composite with a tunable nitrogen doping content in the carbon layer

Abstract

A strategy for the preparation nitrogen-doped carbon encapsulated Si nanocomposite with a void layer (Si@void@NC) is proposed, in which the nitrogen doping content in the carbon layer is tunable. Aniline and ortho-phenylenediamine are both selected as the nitrogen, carbon sources and co-polymerized on Si@SiO2, in which SiO2 is functionalized as a void template. SEM and TEM observation show that Si nanoparticles are encapsulated in a hollow and interconnected carbon cages with a thickness of less than 10 nm, which is inclined to agglomerate together to form larger particles in micrometer scale. The variation of mole ratio of aniline and ortho-phenylenediamine will enable the change of nitrogen doping level in the carbon layer and ranges from 3.2% to 8.4%. The nitrogen is doped into the carbon framework in the form of pyridinic, pyrrolic and graphitic nitrogen. Electrochemical tests indicate that the nitrogen content influences the SEI formation and the lithiation of Si nanoparticles. The potential for the decomposition of electrolyte to form SEI film and the alloying of Si-Li negatively shift when the nitrogen doping content is increased. Furthermore, the cycling performance of Si@void@NC is improved when raising the nitrogen content in the carbon. And the optimal nitrogen content is 7.5%, which is corresponding to the mole ratio of aniline to ortho-phenylenediamine is 5:5.