Lab-scale chemical vapor deposition onto powders

Abstract

In this paper, a laboratory chemical vapor deposition (CVD) reactor is described, which features an opposing screw rotating fluidized bed. The reactor efficiently concentrates powdered reactants in the reaction zone while maintaining fluidization independent of powder properties. This allows for lab-scale CVD processing of many small powder samples at high yields and without the need for re-adjustment of fluidization parameters for different samples. Alumina and graphite were carbon-coated and characterized in lithium batteries. The deposited carbon layer had a density of 1.84 g/ml and a capacity of 225 mA h/g when cycled between 7 mV and 0.9 V in lithium cells. Carbon coatings applied by this CVD reactor onto graphite particles were found to be effective at reducing surface reactions during cycling in lithium cells. We suggest that utilization of this opposing screw rotating fluidized bed reactor can effectively apply CVD coatings to small laboratory powder samples, with particular utility for Li-ion battery materials.