1. Thermodynamics of graphite intercalation binary alloys of Li-Na, Na-K, and Li-K from van der Waals density functionals.
- Author
-
Song, Tao, Xie, Yaoping, Chen, Yigang, and Guo, Haibo
- Subjects
BINARY metallic systems ,DENSITY functionals ,GRAPHITE ,THERMODYNAMICS ,LITHIUM-ion batteries ,GRAPHITE intercalation compounds ,CLATHRATE compounds - Abstract
Graphite may store lithium or potassium, but not sodium, in its interlayer space under ambient conditions. It is, however, unclear whether binary alkali alloys of Li-Na, Li-K, and Na-K may substitute pure Li or K to form binary alkali alloy-graphite intercalation compounds. We investigate thermodynamics of the binary alloy-graphite intercalation compounds using density functional theory with van der Waals density functionals. We find Li-rich co-intercalation compounds and K-rich ones are associated with negative formation energies, and the Na-K alloy has the broadest domain of co-intercalation (approximately up to 36% Na). Because of convexity of the formation-energy functions, these compounds are metastable and tend to decompose even when formation energies are negative. Na metal is among the decomposition products. Binary Li-K alloys in graphite form segregated phases of LiC
6 and KC8 , and this allows one to fabricate Li-K mixed-ion batteries using graphite anodes, whereas Li-Na and Na-K alloys are thermodynamically unfavorable. The study highlights the importance of convexity of formation-energy functions in thermodynamics of alloy-graphite intercalation compounds. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF