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Z. Naturforsch. 69a, 122 – 128
(2014)
doi:10.5560/ZNA.2013-0085
Estimation of Reduced Partition Function Ratios of Lithium-Graphite Intercalation Compounds by Density Functional Theory
Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyodaku, Tokyo 102-8554, Japan
Received August 21, 2013 / revised November 16, 2013 / published online February 5, 2014
Reprint requests to: S. Y.; E-mail:
syan@ea.mbn.or.jp
The reduced partition function ratio (RPFR) of lithium in lithium-graphite intercalation compounds (Li-GICs) was evaluated at the UB3LYP/6-311G(d) level of theory. The partition functions were written in the usual rigid-rotor harmonic oscillator approximation. With a C24H12 coronene molecule as the model of graphene, lithium-coronene sandwich, and club sandwich compounds were considered as models of Li-GICs. The estimated value of the 6Li-to-7Li RPFR was 1.0402 at 25 °C, which yielded 1.034 as the value of the equilibrium constant, K, of the lithium isotope exchange reaction between a lithium ion in an ethylene carbonate/ethylmethyl carbonate mixed solvent and a lithium atom in interlayer space of graphite. The estimated value of K was larger than the experimental
value of 1.025. The unsatisfactory agreement between the estimated and experimental K values suggested that larger molecules should be used as models of graphene and that the vibrational anharmonicity should also be taken into consideration.
Key words: Lithium Graphite Intercalation Compounds (Li-GICs), Lithium Isotopes, Reduced Partition Function Ratio (RPFR), Density Functional Theory, Lithium Isotope Exchange Reaction.