Cation and vacancy ordering in Li{sub x}CoO{sub 2}
- National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
Using a combination of first-principles total energies, a cluster expansion technique, and Monte Carlo simulations, we have studied the Li/Co ordering in LiCoO{sub 2} and Li-vacancy/Co ordering in the {open_square}CoO{sub 2}. We find: (i) A ground-state search of the space of substitutional cation configurations yields the CuPt structure as the lowest-energy state in the octahedral system LiCoO{sub 2} (and {open_square}CoO{sub 2}), in agreement with the experimentally observed phase. (ii) Finite-temperature calculations predict that the solid-state order-disorder transitions for LiCoO{sub 2} and {open_square}CoO{sub 2} occur at temperatures ({approximately}5100 K and {approximately}4400 K, respectively) much higher than melting, thus making these transitions experimentally inaccessible. (iii) The energy of the reaction E{sub tot}({sigma},LiCoO{sub 2}){minus}E{sub tot}({sigma},{open_square}CoO{sub 2}){minus}E{sub tot}(Li,bcc) gives the average battery voltage {bar V} of a Li{sub x}CoO{sub 2}/Li cell for the cathode in the structure {sigma}. Searching the space of configurations {sigma} for large average voltages, we find that {sigma}=CuPt [a monolayer {l_angle}111{r_angle} superlattice] has a high voltage ({bar V}=3.78 V), but that this could be increased by cation randomization ({bar V}=3.99 V), by partial disordering ({bar V}=3.86 V), or by forming a two-layer Li{sub 2}Co{sub 2}O{sub 4} superlattice along {l_angle}111{r_angle} ({bar V}=4.90 V). {copyright} {ital 1998} {ital The American Physical Society}
- OSTI ID:
- 567069
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 57, Issue 4; Other Information: PBD: Jan 1998
- Country of Publication:
- United States
- Language:
- English
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