A time of flight technique was developed to study the C-60 reduction in a solid polymer electrolyte. We have demonstrated that the crystalline C-60 electrochemical irreversibility can be attributed to the crystal dissolution. Furthermore, we found a surprisingly high diffusion coefficient D for all C-60(n-) (n greater than or equal to 4) anionic species in polyethylene oxide with D greater than or equal to 1.8 X 10(-9) cm(2) s(-1) at 80 degreesC. This technique is promising for investigating the electrochemical stability of any intercalation compound where electrode dissolution is suspected.