Intercalation Compounds from LiH and Graphite: Relative Stability of Metastable Stages and Thermodynamic Stability of Dilute Stage I-d
Number of Authors: 3
2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 7, 2566-2575 p.Article in journal (Refereed) Published
The intercalation of lithium into graphite was studied at temperatures between 400 and 550 degrees C by heating mixtures of LiH and graphite powders with molar ratios 4:1, 1:1, and 1:6 under dynamic vacuum for periods between 1 and 72 h. These conditions probe the formation and thermal stability of metastable staged Ligraphite intercalation compounds (Li-GICs) close to the competing formation of the thermodynamically stable carbide Li(2)C2. Li-GICs of stages I (LiC6, A alpha), IIa (Li0.5C6, A alpha A), IIb (Li similar to C-0.33(6), A alpha AB beta B), III (Li similar to C-0.22(6), A alpha AB), IV (Li similar to C-0.167(6)), and dilute stage lithium Id have been identified and characterized by powder X-ray diffraction and Raman spectroscopy. The rate and extent of intercalation (i.e., the achieved stage of Li-GIC) depends on LiH activity and temperature. Stage I was only observed for temperatures above 500 degrees C. At 400 degrees C, the highest intercalation corresponded to stage IIb, which was obtained after 2 and 24 h for 4:1 and 1:1 reaction mixtures, respectively. Lower-staged Li-GICs attained at temperatures below 500 degrees C deintercalate upon prolonged dwelling with the exception of stage IIa, which can be maintained for very long periods (several days) in the presence of LiH. At temperatures above 500 degrees C, the kinetically controlled formation of Li-GICs is followed by Li2C2 carbide formation. It is shown that the Li-GIC I-d coexists with Li2C2 at temperatures up to 800 degrees C and that the Li content of I-d (solubility of Li in graphite) increases between 550 and 800 degrees C. Consequently, I-d with a temperature-dependent homogeneity range should be added as a stable phase in the Li-C phase diagram. A sketch of a revised Li-C phase diagram is provided.
Place, publisher, year, edition, pages
2015. Vol. 27, no 7, 2566-2575 p.
Chemical Sciences Materials Engineering
Research subject Materials Chemistry
IdentifiersURN: urn:nbn:se:su:diva-117731DOI: 10.1021/acs.chemmater.5b00235ISI: 000353176100038OAI: oai:DiVA.org:su-117731DiVA: diva2:818899