Chemical Diffusion Coefficient of Lithium in Carbon Fiber

Electrochemical investigations on coal pitch‐based carbon fiber (heat‐treated at 2800°C) were carried out. The open‐circuit voltages of the Li | Li x C 6 cell were lower than 0.15 V vs. Li / Li + in the range of 0.15 < x < 0.65. The open‐circuit voltage profile vs. x showed no distinct two‐phase region in the present Li‐carbon system in 0 < x < 0.65. Almost constant capacity of 220 mAh/g was observed until the 140th cycle in the cycling tests of the Li|carbon fiber cell (current density 25 mA/g) The compositional variation of the chemical diffusion coefficient of lithium D ̃ Li at ambient temperature was measured by two different methods, i.e. , the current pulse relaxation method and the potential step chronoamperometric method. Excellent agreement within one order of magnitude was observed between the two sets of D ̃ Li values obtained from these two methods. The values were around 10 − 9.5 cm 2 / s at x ≒ 0 and decreased with increasing x . The D ̃ Li values lay between 10 − 11 and 10 − 12 cm 2 / s in x > 0.2