Laser pyrolysis synthesis of Sn–Fe–N@polycarbosilazane nanocomposites, characterization and evaluation as energy storage materials

We report the single-step synthesis of novel tin-based core–carbosilazane shell nano-composites using laser pyrolysis technique. Controlled NH 3 flows were used to entrain the vapors of volatile precursors: Sn(CH 3 ) 4 (TMT) and Fe(CO) 5 injected through center for the core and [Si(CH 3 ) 3 ] 2 NH (HMDS) through the annular nozzle for the shell. Both NH 3 and HMDS plays also the role of absorbers of the IR laser radiation. The obtained nanoparticles shown polydispersity with sizes from 5 up to around 120 nm, having spheroidal crystalline core—disordered shell morphology as confirmed by transmission electron microscopy images, where also short amorphous nanofibers were observed. The dominant crystalline phase β-Sn (having mean crystallite size between 22 and 29 nm) and minor tin-iron intermetallic and nitride phases were identified by X-ray diffraction. Infrared spectra show the presence of Si–N and Si–C bonds, pointing to a carbosilazane composition of the shells, accompanied by Si–O bonds due to partial oxidation after air exposure. Three different samples were obtained by keeping constant the Sn and Fe precursors flows and diminishing the HDMS flow, together with the corresponding NH 3 flows. Preliminary tests of these materials as anodes for Li-ion battery showed an initial discharge capacity near 800 mAg/h which decreased to 300 mAh/g after 20 cycles for the sample having the highest Sn content.