(An) investigation of the electrochemical lithium intercalation reaction into transition metal oxides $Li_{1-δ}MO_2$ (M=Ni, Co, Mn)

Abstract

The present work is concerned with the electrochemical lithium intercalation reaction into transition metal oxides $Li_{1-\delta}MO_2$ (M=Ni, Co, Mn). In chapter III, the effects of cation mixing on electrochemical lithium intercalation reaction into porous $Li_{1-\delta}Ni_{1-y}Co_yO_2$ electrodes in 1 M $LiClO_4$ propylene carbonate(PC) solution have been investigated by using electrochemical impedance spectroscopy(EIS) as functions of lithium content (1-$\delta$) and cobalt content y. The electrochemical lithium intercalation behaviour of porous $LiNiO_2$ electrodes prepared by solid-state reaction and sol-gel methods have been examined by using X-ray diffractometry(XRD), galvanostatic intermittent charge-discharge experiment, electrochemical impedance spectroscopy(EIS) and charge-discharge cycling test. The conventional oxide electrode showed a larger capacity loss, a greater instantaneous IR drop during the first intermittent discharge and a smaller chemical diffusivity than the gel-derived electrode. The results have been discussed with respect to the marked cation mixing effect in the former electrode. Furthermore the charge-discharge cycling test of the cell Li/organic electrolyte/gel-derived $LiNiO_2$ electrode exhibited an improved cell performance, the initial specific capacity of 150 Ah/kg and energy density above 500 Wh/kg. In chapter IV, the lithium transport through porous $Li_{1-\delta}CoO_2$ electrode has been studied by using potentiostatic current transient technique. The measured current transients were analysed in terms of the phase boundary movement based upon the concept of the quasi-equilibrium established by the open-circuit potential transient measurement. The scaling of the current and the time was performed with respect to the driving force and transferred charge by using the values of the quasi- equilibrium potential and the corresponding lithium stoichiometry. The scaled current transients consist of three stages and agree satisfac...