Li diffusion properties of mixed conductingTiO2-Bnanowires

Abstract

${\text{Li}}_{x}{\text{TiO}}_{2}\text{-B}$ nanowires $(0lx\ensuremath{\le}0.9)$ are considered to act as promising anode materials in secondary Li-ion batteries. Li self-diffusion parameters in mixed conducting nanowires of the composition ${\text{Li}}_{0.3}{\text{TiO}}_{2}$ are directly determined by mixing time $({t}_{m})$-dependent two-time $^{7}\text{L}\text{i}$ spin-alignment echo (SAE) nuclear-magnetic-resonance (NMR) correlation spectroscopy between 330 and 500 K. SAE NMR reveals extremely slow Li self-diffusion processes in ${\text{Li}}_{x}{\text{TiO}}_{2}\text{-B}$. Li jump rates ${\ensuremath{\tau}}^{\ensuremath{-}1}$ range from 5 to $2.5\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }{\text{s}}^{\ensuremath{-}1}$. The corresponding hopping correlation functions ${F}_{2}$ can be well parametrized with stretched exponentials, ${F}_{2}\ensuremath{\propto}\text{exp}[\ensuremath{-}{(t/{t}_{m})}^{\ensuremath{\gamma}}]$, with an exponent $\ensuremath{\gamma}=0.35(2)$ being independent of temperature. The influence of spin-diffusion effects on the echo amplitude is elaborated by evolution time-dependent $^{7}\text{L}\text{i}$ SAE-NMR experiments. The results are compared with those obtained by conventional $^{7}\text{L}\text{i}$ NMR spin-lattice relaxation measurements.