(The) kinetics of lithium transport through the graphite and hard carbon electrodes

Abstract

The present work is concerned with the kinetics of lithium transport through the graphite electrode with a high degree of crystallinity and the hard carbon electrode with a low degree of crystallinity. In chapter III, the kinetics of lithium transport through the graphite electrode with a high degree of crystallinity has been investigated in a 1M LiPF6-ethylene carbonate(EC) / diethylene carbonate(DEC) (1:1 by vol.%) electrolyte using galvanostatic intermittent titration technique, ac-impedance spectroscopy and potentiostatic current transient technique. All the anodic current transients experimentally measured on the SFG6 graphite composite electrode hardly follow the Cottrell behaviour during the whole lithium deintercalation. Moreover, the initial current level of the current transient is linearly proportional to the applied potential step. These experimental findings can be reasonably simulated under the `cell-impedance-controlled`` constraint. Thus, it is strongly asserted that the flux of the lithium ion at the electrode/electrolyte interface during lithium transport through the SFG6 graphite electrode is purely governed by `cell-impedance`` . In chapter IV, in order to investigate the effect of microstructure change of carbon on the lithium transport through the carbon, we extended our research work to the lithium transport through hard carbon electrode with a low degree of crystallinity. The anodic current transients at various electrode potentials simulated based upon the modified McNabb-Foster equation as a governing equation, and the `cell-impedance-controlled`` constraint as a boundary condition coincide fairly well with the corresponding current transients experimental measured on the disordered carbon composite electrode, with regard to the non-Cottrell character and the presence or absence of inflexion point of `quasi-current plateau``. This strongly indicates that the lithium transport through the hard carbon electrode is also governed by the `c...