Li mobility in the battery cathode materialLix[Mn1.96Li

The battery cathode materials ${\mathrm{Li}}_{x}[{\mathrm{Mn}}_{1.96}{\mathrm{Li}}_{0.04}]{\mathrm{O}}_{4}$ with $x=1$ and 0.2 were studied by the zero-field muon-spin-relaxation technique. Both materials have a magnetic transition below ${T}_{\mathrm{M}}\ensuremath{\simeq}25 \mathrm{K}.$ At high temperature, above $T=230 \mathrm{}\mathrm{K},$ a large decrease of the width of the static field distribution at the muon site is found for $\mathrm{Li}[{\mathrm{Mn}}_{1.96}{\mathrm{Li}}_{0.04}]{\mathrm{O}}_{4},$ providing proof of the onset of mobility of ${\mathrm{Li}}^{+}$ ions in the microsecond time range. On the other hand, in ${\mathrm{Li}}_{0.2}[{\mathrm{Mn}}_{1.96}{\mathrm{Li}}_{0.04}]{\mathrm{O}}_{4}$ the onset of mobility of ${\mathrm{Li}}^{+}$ ions occurs only for $T>300 \mathrm{K},$ i.e., just above room temperature.