Lithium ion diffusion through glassy carbon plate

摘要

The electrochemical permeation method was applied to the determination opf the diffusion coefficient of Li~(+ ion (D_(li~+)) in a glassy carbon (GC) plate. The cell was composed of two compartments, which were separated by the GC plate. Li~+ ions were inserted electrochemically from one face, and extracted from the other. The flux of the permeated Li~+ ions was monitored as an oxidation current at the latter face. The diffusion coefficient was determined by fitting the transient current curve with a theoretical one derived from Fick'slaw. When the potential was stepped between two potentials in the range of 0 to 0.5 V, transient curves were well fitted with the theoreetidal one, which gave D_(Li~+)values of the order of 10~(-8) cm~2 s~(-1). In contrast, when the potential was stepped between two potentials across 0.5 V, significant deviation was observed. The deviation indicated the presence of trap sites as well as diffusion sites for Li~+ ions, the former of which is the origin of the irreversible capacity of GC.