A method of compacting material such as but not limited to cathode material for electrochemical cells. A mixture is inserted into a die cavity and the mixture is compacted into a disk shape by the action of a first plunger pressing down on the material and a second plunger pressing upwardly on the material. Flashing of material during ejection of the disk from the die is prevented by fitting a polymeric sleeve around the outer surface of the first plunger. The sleeve flexes to bulge outwardly and does not enter the die cavity during compaction of material and returns to its original position during ejection of the compacted disk from the die. Contact between the disk and sleeve prevents flashing during ejection. Alternatively, a polymeric seal ring is placed around the outer surface of the first plunger. The disk presses against the seal ring preventing flashing of material during ejection.