A computational investigation on fluorinated-polyanionic compounds as positive electrode for lithium batteries

• Published in: Journal of power sources 2007-12, Vol.174 (2), p.1251-1257
• Main Authors: de Dompablo, M.E. Arroyo y, Amador, U., Tarascon, J.-M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrode materials; Exact sciences and technology; First principles calculation; Fluorine compounds; Lithium batteries; Olivine
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2007.06.178

First principles calculations have been used to investigate the effect of fluorine substitution on the electrochemical properties of Li 2VOSiO 4 and LiFePO 4. Several models of hypothetical LiVSiO 4F and Li 0.5FePO 3.5F 0.5 within the structure of the corresponding parent compounds have been analyzed. The computational results indicate that the lithium insertion voltage is largely controlled by the crystallographic site that fluorine ions occupy in the structure. In some models of LiVSiO 4F and Li 0.5FePO 3.5F 0.5 lithium deinsertion causes a too large M–F distance (indicative of M F bond breaking), being the predicted lithium insertion voltage about 0.3 V lower than that of the parent compound. In the energetically most stable model of hypotetical-LiVSiO 4F the V F bond is retained, and a voltage increasing of 0.5 V is predicted with respect to that of the parent compound. For hypothetical Li 0.5FePO 3.5F 0.5 models consisting on FeO 6 and FeO 4F 2 octahedra the lithium deinsertion produces solely the oxidation of Fe 2+ surrounded by oxygen ions, which is accompanied by a voltage decreasing. These findings are supported by the computational results on the known intercalation compound LiVPO 4F.