Lithium electrochemical deintercalation from O2-LiCoO2: structure and physical properties
Résumé
Electrochemical deintercalation of Li from the metastable O2-LiCoO2 phase has been investigated up to the composition Li0.15CoO2. The single-phase domains that separate the voltage plateaus observed have been characterized by X-ray diffraction. The succession of phases observed upon deintercalation results from reversible sheet gliding or lithium/vacancy ordering, leading to the sequence 02, T#2, T#2', 06, 02, 02. In particular, the T#2 stacking, similar to the T2 phase reported by Dahn and co-workers for the Li2/3Ni1/3Mn2/3O2 phases, corresponds to oxygen ions not sitting on the three positions of a triangular lattice, hence the # character is used. It exhibits very distorted tetrahedral sites for Li. The 06 stacking exhibits two kinds of CoO6 octahedra, which might allow Co3+/Co4+ ordering in alternate sheets. The most deintercalated O2-Li0.15CoO2 phase has never been reported before. Electronic properties and 7Li magic-angle spinning nuclear magnetic resonance show a transition to a metallic state for x< 0.94 (appearance of the T#2 phase with x = 0.72). These stacking changes are proposed to result from the minimization of electrostatic repulsion, except for T#2' (x = 0.50), which is believed to result from a Li/vacancy ordering.
Mots clés
Transition metal Compounds
Alkali metal Compounds
Lithium
X ray diffraction
NMR spectrometry
Specific capacity
Discharge charge cycle
Electrical characteristic
Crystal morphology
Electronic properties
Lattice parameters
Crystalline phase
Lithium oxide
Cobalt oxide
Intercalation compound
Ternary compound
Electrode material
Electric batteries
Domaines
Matériaux
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