Tunable Anisotropic Thermal Conductivity and Elastic Properties in Intercalated Graphite via Lithium Ions

ZY Wei and F Yang and KD Bi and JK Yang and YF Chen, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 1447-1455 (2018).

DOI: 10.1021/acs.jpcc.7b09717

The electrochemical intercalation of metal ions into layered materials is a useful strategy to reversibly tune thermal-transport properties, but the fundamental mechanisms are not well understood. In this study, we systematically investigated the effects of lithium-ion concentrations on the anisotropic thermal conductivity of intercalated graphite by molecular-dynamics simulations and a continuum-mechanics method. It was found that the in-plane thermal conductivity rapidly decreased to 34.3% of that of graphite in the same direction when the lithium-ion concentration increases to 0.1667. However, the cross-plane thermal conductivity first decreased to 23.7% of that of the graphite. Then, it surprisingly recovered to a thermal conductivity even higher than that of graphite when the lithium-ion concentration increased further. These two different trends and thermal-conductivity anisotropies were explained by extracting the phonon lifetimes and elastic constants of intercalated graphites with various lithium-ion concentrations. At lithium-ion concentrations lower than 0.05, the reduction of both the in-plane and cross-plane thermal conductivities in the intercalated graphite was attributed to the increased phonon scattering owing to the interactions between the lattices and ions. However, at lithium concentrations higher than 0.05, the thermal transport of the intercalated graphite was mainly influenced by anisotropic elastic constants. The rapidly increasing cross-plane elastic constants increased the cross-plane thermal conductivity, while simultaneously weakening the phonon focusing effects along the in-plane direction, which resulted in the opposite tendencies of the in-plane and cross- plane thermal conductivities with increasing lithium-ion concentrations. This study provides important guidance in the active regulation of the anisotropic thermal conductivities of layered materials for thermal management in energy storage and conversion.

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