NA-23-NMR STUDIES OF NAXCOO2 CATHODE MATERIALS

Two samples of oxidized sodium cobalt oxide, NaxCoO2, where x=0.3 and 0.7, have been studied by variable-temperature wide-line Na-23-NMR. Al l spectra exhibit a substantially paramagnetic-shifted response charac terized by 2nd-order quadrupole broadening and a diamagnetic-shifted w eaker response. The paramagnetic shifts are attributed to spins locali zed on cobalt atoms. The 2nd-order quadrupolar splitting is resolved f or x=0.7; whereas the lineshapes obtained for x=0.3 do not show the re solution and indicate a more symmetric sodium environment and/or a gre ater degree of ion mobility, Lineshapes for the two compositions behav e somewhat differently as the temperature is changed, although both sa mples exhibit gradual line-narrowing over the entire range (-150 to 10 0 degrees C). Spin-lattice relaxation time measurements reflect the pr esence of inequivalent sodium environments, with one distribution of s odium environments characterized by long relaxation times (10 ms-200 m s) and another set of environments characterized by much shorter times (< 500 mu s).