Tracer diffusion coefficients of lithium ion in LiMn_2O_4 measured by neutron radiography

摘要

Lithiumisotope diffusion profiles in the cathodematerial LiMn_2O_4 have been measured by using neutron radiography technique to determine the tracer diffusion coefficients D* in the temperature range of 300 °C to 800 °C. Arrhenius plot of the diffusion coefficient shows a bend around 550 °C. At the lower temperature region, the activation energy of the diffusion coefficient is obtained as 0.52 eV, which is essentially consistent with that of the reported NMR study. However, the extrapolated diffusion coefficient down to room temperature is considerably smaller than the chemical diffusion coefficients obtained by electrochemical methods. On the other hand, hightemperature activation energy of 1.11 eV is relatively close to the previously investigated Li_4Ti_5O_(12), which also exhibits spinel-type structure and possesses the similar diffusion path via the 16c site. Within the present study, sintering temperature at the LiMn_2O_4 sample preparation does not affect the tracer diffusion coefficient values.