Electronic Structure of Chemically-Delithiated LiCoO₂ Studied by Electron Energy-Loss Spectrometry

Abstract

The electronic structure of chemically delithiated Li1 - x CoO2 (x = −0.02, 0.09, 0.12, 0.20, and 0.28) was investigated by electron energy-loss spectrometry (EELS). The O K edge and Co L2,3 edge were used to probe the density of unoccupied states around the O and Co ions at different states of lithiation. The O ions accommodate the incoming charge during Li intercalation. The net electron density surrounding the Co ions is less affected. This is in substantial agreement with prior electronic structure calculations of Van der Ven, et al., whose atomic structure data were used in the present calculations of EELS cross-sections. Calculations of the O 2p partial densities of state curves confirm the increase in unoccupied states that accompany Li extraction.

Synthesis and Characterization of LiCoO2 from Different Precursors by Sol‑Gel Method

“…[1][2][3][4][5][6][7][8] This system has interesting electrochemical features that allows a wide use as cathodes of lithium ion batteries. 2,4 The investigation of the structural aspects of the material is a crucial issue to better understand the electrochemical properties of the LiCoO 2 compound.…”

“…2,4 The investigation of the structural aspects of the material is a crucial issue to better understand the electrochemical properties of the LiCoO 2 compound. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] For example, the nature of the crystal, its size and shape, are directly related with its electrochemical characteristics. 2 The LiCoO 2 synthesized at low temperatures (LT), below 500 °C, presents a cubic spinel structure ( ), while the synthesis at high temperatures (HT) (above 500 °C), generates the rhombohedral structure with stratified layers ( ).…”

“…Finally, the lithium layers are intercalated between the CoO 2 plans. 1,3,4 The octahedral sites of these layers are occupied by lithium and cobalt(III) ions alternately that forms a sequential stacking with oxygen ion layers in a close packing of the ABCABC type ( Figure 1c). 4,5 This specific stacking arrangement leads to an environment equivalent for all ions, allowing the maximum charge delocalization and the minimal system energy.…”

“…4,5 This specific stacking arrangement leads to an environment equivalent for all ions, allowing the maximum charge delocalization and the minimal system energy. 1,3,4 The degree of crystal order, the particle size distribution and the average particle size depend on the starting materials and the preparation method. 18 For this reason, the sol-gel method has been widely used modulating these properties.…”

White lines andd-band occupancy for the3dtransition-metal oxides and lithium transition-metal oxides

“…Other research has been driven by the success of the lithiated transition-metal oxides as cathodes in rechargeable lithium batteries. A number of x-ray absorption and EELS experiments have been performed to investigate charge compensation during electrochemical cycling of lithium 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19 17 and it is unclear how much charge is transferred to each transition-metal ion. It is our contention that changes in the transitionmetal valence can be measured quantitatively using the transition-metal white lines.…”