Intercalation reactions and carbide formation in graphite-lithium system

Abstract

Abstract In the present work we have investigated a lithium-graphite system by DTA, DSC, heat flow calorimetric, and volumetric methods in a “piston-cylinder apparatus” under high pressures (23 kbar). For the first time, we have determined the enthalpies (ΔHform) of LiC6 (1 stage) and LiC12 (2 stage) formation by the direct calorimetric method at 455 K. It was stated that the values are −13.9 ± 1.2 kJ/mol Li and −24.8 ± 1 kJ/mol Li, respectively. We have defined the enthalpies and temperatures of (3D) → (2D) transitions in LiC6 (T = 711 ± 5 K, ΔHph.tr. = 1.1 ± 0.3 kJ/mol Li) and in LiC12 (T = 472 ± 5K, ΔHph.tr = 1.45 ± 0.2 kJ/mol Li). The rhombohedral modification of Li2C2 was explored at T = 293–1000 K. Only one phase transition at T = 716 ± 6 K (ΔHph.tr. = 5.56 ± 0.09 kJ/mol Li2C2) was detected. The compressibility of Li2C2 was investigated at pressures up to 23 kbar and at room temperature. The change of molar volume ( ΔV V 0 , % ) was −2.07 ± 0.07 (10 kbar) and −3.46 ± 0.14 (22 kbar). We studied the carbide formation in Li-GICs at ambient and high pressure (P = 60 kbar) as well.