Studies of Li and Mn-Rich Li-x MnNiCo O-2 Electrodes: Electrochemical Performance, Structure, and the Effect of the Aluminum Fluoride Coating

We report herein on the study of Li and Mn rich Li-x[MnNiCo]O-2 cathode materials with an emphasis on the effect of AlF3 coating on their electrochemical performance. The initial stoichiometry of these materials was xLi(2)MnO(3)center dot(1-x)LiMnyNizCowO2 where x is in the range 0.4-0.5 and the y:z:w ratio was as we previously reported. Their structure was considered on the basis of two-components model, namely monoclinic Li2MnO3 (C2/m) and rhombohedral LiMO2 (R-3m) (M = Mn, Ni, Co) that are structurally compatible and closely integrated phases. Based on TEM studies we concluded that the coating had a crystalline tetragonal structure t-AlF3 (P4nmm symmetry) and AlF3 nano-crystals were regularly distributed over the particles surface. Amorphous clusters of AlF3 and/or other Al-containing species, like AlFxOy, Al[FOH], etc. may also present, as it follows from solid-state NMR measurements. It was shown that electrodes comprising the AlF3-coated material exhibited higher reversible capacities of similar to 250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60 degrees C, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Li-x[MnNiCo]O-2/AlF3 materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts. (C) 2013 The Electrochemical Society. All rights reserved.

Last Updated Date : 14/01/2015