Electrochemical insertion of lithium ions into disordered carbons derived from reduced graphite fluoride

• Published in: Carbon (New York) Vol. 41; no. 3; pp. 453 - 463
• Main Authors: Giraudet, J, Dubois, M, Inacio, J, Hamwi, A
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2003; Elsevier Science
• Subjects: A. Graphite; Applied sciences; B. Chemical treatment; D. Electrochemical properties; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Heat treatment; Intercalation compounds; B. Chemical treatment; Heat treatment; D. Electrochemical properties; A. Graphite; Intercalation compounds; Intercalation compound; Electrochemical properties; Anode; Chemical treatment; Lithium batteries; Secondary cell; Electrode material; Carbon fluorides
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/S0008-6223(02)00341-X

Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO
4–EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F
2 atmosphere for 2 h at 150
°C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g
−1 in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li
+/Li limiting the useful capacity.