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

• NMR study of two SiCN polymer-derived ceramics was carried out.
• Free carbons act as major electrochemically active sites for Li storage.
• An additional path for Li storage can be formed through the mixed tetrahedra of Si.
• The activation energy 0.31 eV and the correlation time at infinite temperature 1.3 ps were deduced.
• The Li motion is governed by continuum diffusion mechanism given by the uniquely determined diffusion parameters.

We report 7Li, 29Si, and 13C 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 13C 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 (ωLωL) dependences of the 7Li linewidth and spin-lattice relaxation rates T1−1 are described by an activated law with the activation energy EAEA of 0.31 eV and the correlation time τ0τ0 in the high temperature limit of 1.3 ps. The 3/23/2 power law dependence of T1−1 on ωLωL which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the μ  s timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T1ρ−1 results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes.