On the role of defects in decreasing the extra 3.3/3.95 and 4.5 V redox steps in Li-Mn-O spinels

LiMn2O4 spinels were studied with the aim of assessing the role of differen t types and amounts of defects in blocking the phase transition from spinel to double hexagonal that is associated with anomalous 4.5 and 3.3/3.95 V r edox steps, The influence of the type of MnO2 precursor (beta or gamma, bot h with diverse amounts of stacking faults), the effect of introducing defec ts in the final spinel by ball milling or of cationic subsitutions on the s pinel 16d sites (Al or Li) were examined. Electrochemical experiments perfo rmed on all these defective samples indicate: that defects block the phase transition to a certain extent. The introduction of either Li or Al in spin el 16d sites proved to be the most effective to prevent the structural tran sformation, and thus eliminate the anomalous redox steps that are detriment al to the electrochemical performances of LiMn2O4. (C) 2001 Elsevier Scienc e B.V. All rights reserved.