Abstract
Direct observation of delithiated structures of LiCoO2 at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO2 nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO2, the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO2 to O1-type LixCoO 2 (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type LixCoO2 (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-LixCoO2 in the phase diagram of O3-LiCoO2, through which the two previously separated LiCoO 2 phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.
Original language | English |
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Pages (from-to) | 6192-6197 |
Number of pages | 6 |
Journal | Nano Letters |
Volume | 12 |
Issue number | 12 |
DOIs | |
Publication status | Published - 2012 Dec 12 |
Externally published | Yes |
Keywords
- Li-ion batteries
- LiCoO
- scanning transmission electron microscopy (STEM)
- structural evolution
ASJC Scopus subject areas
- Bioengineering
- Chemistry(all)
- Materials Science(all)
- Condensed Matter Physics
- Mechanical Engineering