Method for preparing silicon-carbon-graphene composite, composite prepared according thereto, and secondary battery to which same is applied

A manufacturing method of a silicon-carbon-graphene composite, comprising.

• acid-leaching a waste silicon sludge, and selectively separating and recovering silicon by ultrasonic treatment and centrifugal separation in step 0;
• adding a carbon precursor solution to the recovered silicon and performing wet pulverization to prepare a suspension in step 1;
• forming a silicon-carbon composite by ultrasonically spray-drying the suspension in step 2;
• spraying a mixed solution of the silicon-carbon composite and graphene oxide in a form of aerosol droplets through a two-fluid nozzle in step 3a;
• and
• drying and heat-treating the sprayed droplets by passing the sprayed droplets through a tubular heating furnace via a carrier gas in step 3b.