Electrochemical properties of spinel Li{sub x}CoO{sub 2}: A first-principles investigation

Journal Article · Fri Jan 01 00:00:00 EST 1999 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.59.742· OSTI ID:289181

Van der Ven, A; Ceder, G ^[1]

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1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States)

We present the results of a first-principles study of the electrochemical and lithium ordering properties of spinel Li{sub x}CoO{sub 2} for {ital x} ranging from 0 to 1. The spinel form of Li{sub x}CoO{sub 2} belongs to the Fd3m space group and can accommodate Li ions in two crystallographically distinct sites: the tetrahedrally coordinated 8a sites and the octahedrally coordinated 16c sites. We have investigated a lattice model for this system derived from first principles that allows for the simultaneous occupation by Li of both these sites. The calculated voltage intercalation curve of this phase exhibits a step of more than a volt at {ital x}=1/2. This step is a result of the large stability of ordered spinel Li{sub 1/2}CoO{sub 2} in which the Li ions fill all the tetrahedral 8a sites. The remarkable stability of this ordered phase produces a sharp curvature in the free energy at x=1/2 that translates into an abrupt change in the voltage curve. As the temperature is raised, the voltage step gradually disappears as a result of the increased excitations of Li ions into energetically less favorable octahedral sites. We have also calculated the phase diagram for spinel Li{sub x}CoO{sub 2}. A miscibility gap is predicted between x=0.5 and x=1.0. At x=1/4, Li is predicted to order below approximately 150 K. This ordering causes a small step of about 0.2 V similar to that observed in spinel Li{sub x}MnO{sub 2} at room temperature for {ital x} in the vicinity of 1/4. {copyright} {ital 1999} {ital The American Physical Society}

• OSTI ID: 289181
• Journal Information: Physical Review, B: Condensed Matter, Vol. 59, Issue 2; Other Information: PBD: Jan 1999
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
LITHIUM COMPOUNDS
PHASE DIAGRAMS
LITHIUM OXIDES
COBALT OXIDES
ELECTROCHEMISTRY
ORDER-DISORDER TRANSFORMATIONS
SPINELS
TEMPERATURE RANGE 0065-0273 K
CRYSTAL-PHASE TRANSFORMATIONS
CRYSTAL DEFECTS
ELECTRIC POTENTIAL
TEMPERATURE RANGE 0273-0400 K
FREE ENERGY
SPACE GROUPS
THERMODYNAMIC PROPERTIES
MONTE CARLO METHOD