A reactor for coating particles includes one or more motors, a rotary vacuum chamber configured to hold particles to be coated and coupled to the motors, a controller configured to cause the motors to rotate the chamber in a first direction about an axial axis at a rotation speed sufficient to force the particles to be centrifuged against an inner diameter of the chamber, a vacuum port to exhaust gas from the rotary vacuum chamber, a paddle assembly including a rotatable drive shaft extending through the chamber and coupled to the motors and at least one paddle extending radially from the drive shaft, such that rotation of the drive shaft by the motors orbits the paddle about the drive shaft in a second direction, and a chemical delivery system including a gas outlet on the paddle configured inject process gas into the particles.