A reactor for coating particles includes a stationary vacuum chamber having a lower portion that forms a half-cylinder and an upper portion to hold a bed of particles to be coated, a vacuum port in the upper portion of the chamber, a paddle assembly, a motor to rotate a drive shaft of the paddle assembly, a chemical delivery system to deliver a first fluid, and a first gas injection assembly to receive the first fluid from the chemical delivery system and having apertures configured to inject a first reactant or precursor gas into the lower portion of the chamber and such that the first reactant or precursor gas flows substantially tangent to a curved inner surface of the half-cylinder.