Structural analysis and electrochemical characteristics of new CxNFz compounds in aprotic media

Carbon-nitrogen-fluorine compounds, CxNFz, were prepared by a two-step-process and their electrochemical behaviour was evaluated in a Li cell. At first, CxN compounds were synthesised by thermal decomposition of acetonitrile in presence of a nickel catalyst. Then, the CxN compounds were fluorinated with fluorine gas at room temperature giving rise to CxNFz, The composition and the structure of CxN and CxNFz samples were determined from elemental analysis, XPS and X-ray diffraction. It was shown that the CxN samples have the same layered structure as usual carbon, contrary to CxNFz samples which present an amorphous structure, The electrochemical properties of C18.7NF5.9 have been investigated in 1 M LiClO4-propylene carbonate at 25 degrees C by discharge-recharge characteristics. The reversibility of the insertion-deinsertion process was pointed out without apparent modification of the host structure. The chemical diffusion coefficient, (D) over tilde(Li), deduced from a galvanostatic intermittent titration method, is roughly constant in all the insertion ratio range and close to 3.3 x 10(-9) cm(2) s(-1) at 25 degrees C. Moreover, the partial conductivity of lithium cations, sigma(Li), was found to be independent on the insertion ratio value and close to 1.4 x 10(-6) Omega(-1) cm(-1). (C) 1999 Elsevier Science Ltd. All rights reserved.