Laser pyrolysis synthesis of nanoparticles for energy applications

Abstract : The laser pyrolysis method has proved efficient for the synthesis of various oxide and non-oxide nanoparticles such as SiC, Si, TiO$_2$... Recently we have developed the method for the one-step production of Si@C core shell nanoparticles and composites of TiO$_2$-carbon nanostructures. Much attention has been paid to Si as an anode material in Li-Ion batteries in order to improve storage capacity (the theoretical limit being 3579 mAh/g in the Li$_{15}$Si$_4$ alloy vs 372 mAh/g for graphitic carbon). However, due large volume changes during cycling, silicon suffers several drawbacks, including rapid pulverization and SEI ripening, limiting its use. Nanostructuration and protection of silicon by a carbon coating are proven methods to improve the behavior of the silicon based anodes. We have developed a two stage laser pyrolysis reactor to achieve the synthesis of silicon-carbon core-shell nanoparticles in a continuous way, without intermediate manipulations between the synthesis of the core and the shell. At lab scale, the reactor is capable of stable run times up to several hours with production rates of ~8-10 g/hour. The size of the core was tuned from 20 to 80 nm diameter with associated carbon content of up to 20 wt%. EIS spectroscopy clearly shows the influence of the carbon coating on the growth of SEI during the first cycle, with a significantly lower resistance of the SEI when Si@C nanoparticles are used by comparison with Si. The carbon coating also enables improved utilization of silicon content in the first cycles as shown by galvanostatic cycling. By adding germane in the reaction zone, we were also able to synthesize nanoparticles of SixGe1-x with x in the range 20-80. These particles also present a core@shell organization with a silicon shell at the surface of the alloy particle. These NPs present improved columbic efficiency and stability when tested in coin cells.