Lithium transport through the Li_(1-δ)CoO_2 film electrode prepared by RF magnetron sputtering

摘要

Lithium transport through the Li_(1-δ)CoO_2 film electrode prepared by RF magnetron sputtering was investigated in a 1 M solution of LiClO_4 in propylene carbonate using the galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), and the potentiostatic current transient technique. The experimental cathodic and anodic current transients in the presence of a single phase Li_(1-δ)CoO_2 did not follows Cottrell behaviour, but Ohmic behaviour. This means the relationship between the initial current level and the potential step obeys Ohm's law. In addition, the current transients obtained in the case of coexistence of two phase α and β were characterised by a flatter shape, as compared to those transients in the presence of the respective α and β phases. Also, during phase transformation, the instantaneous current level was proportional to the potential step, in compliance with Ohm's law. From these results, it was suggested that the flux of lithium ion at the electrode | electrolyte interface during lithium transport is limited purely by the 'cell-impedance', not only in the presence of a single phase, but also when the two phases coexist. The value of the 'cell-impedance' calculated from the current transient was almost equal to the values obtained from the impedance spectra and the galvanostatic discharge curve. The current transients were modelled under the assumption of the 'cell-impedance-controlled' lithium intercalation and deintercalation. The current transients calculated theoretically coincided well in value and shape with those measured experimentally.