Lithium dynamics in carbon-rich polymer-derived SiCN ceramics probed by nuclear magnetic resonance

We report Li-7, Si-29, and C-13 NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei, we find that only the C-13 spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature (T) and Larmor frequency (omega(L)) dependences of the Li-7 linewidth and spin-lattice relaxation rates T-1(-1) are described by an activated law with the activation energy E-A of 0.31 eV and the correlation time tau(0) in the high temperature limit of 1.3 ps. The 3/2 power law dependence of T-1(-1) on omega(L) which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the mu s timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T-1 rho(-1) results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes. (C) 2013 Elsevier B.V. All rights reserved.