Electronic structure of chemically deintercalatedLiCo0.9Ga0.1O2

Abstract

We studied the changes in the electronic structure of $\mathrm{Li}\mathrm{Co}{\mathrm{O}}_2$ induced by 10% Ga substitution. The technique used in the study was $\mathrm{Co}2p$ and $\mathrm{O}1s$ X-ray absorption spectroscopy. The spectra were analyzed using atomic multiplet and band structure calculations. The $\mathrm{Co}2p$ spectra show that the Co ions in $\mathrm{Li}\mathrm{Co}{\mathrm{O}}_2$ are in a trivalent ${\mathrm{Co}}^{3+}$ low-spin state, and that the electronic structure of the Co ions is not greatly affected by 10% Ga substitution. The Co ions remain in the trivalent ${\mathrm{Co}}^{3+}$ low-spin state in chemically deintercalated ${\mathrm{Li}}_x{\mathrm{Co}}_{0.9}{\mathrm{Ga}}_{0.1}{\mathrm{O}}_2$. This shows that the Co ions in deintercalated ${\mathrm{Li}}_x{\mathrm{Co}}_{0.9}{\mathrm{Ga}}_{0.1}{\mathrm{O}}_2$ are not oxidized to a tetravalent ${\mathrm{Co}}^{4+}$ state. The $\mathrm{O}1s$ spectra are dominated by transitions to mixed $\mathrm{O}2p-\mathrm{Co}3d$ states at threshold. The transitions to $\mathrm{O}2p-\mathrm{Ga}4sp$ states appears well above threshold due to the larger hybridization. The $\mathrm{O}1s$ spectra of deintercalated ${\mathrm{Li}}_x{\mathrm{Co}}_{0.9}{\mathrm{Ga}}_{0.1}{\mathrm{O}}_2$ show an increase in the absorption intensity at threshold. The increased $\mathrm{O}1s$ absorption intensity indicates that the $\mathrm{O}$ ions are oxidized in deintercalated ${\mathrm{Li}}_x{\mathrm{Co}}_{0.9}{\mathrm{Ga}}_{0.1}{\mathrm{O}}_2$. The results and conclusions obtained for deintercalated ${\mathrm{Li}}_x{\mathrm{Co}}_{0.9}{\mathrm{Ga}}_{0.1}{\mathrm{O}}_2$ are similar to those for ${\mathrm{Li}}_x{\mathrm{Co}\mathrm{O}}_2$; this shows that the Ga substitution does not significantly affect the charge transfer mechanism in ${\mathrm{Li}}_x{\mathrm{Co}\mathrm{O}}_2$.