Re-Deposition of Manganese Species on Spinel LiMn2O4 Electrode after Mn Dissolution

Re-deposition of manganese compounds on LiMn2O4 electrode after Mn dissolution and its impact on the positive electrode performances are studied by a control experiment, in which the spinel electrode is stored in its charged state at elevated temperature (60 degrees C) to accelerate Mn dissolution. Upon storage with Li foil, the re-deposition of manganese species is marginal since the dissolved Mn2+ ions move to the Li foil to be deposited. When stored without Li foil, however, under which the chance for re-deposition of Mn species on the spinel electrode is rather high, the dissolved Mn2+ ions are deposited as oxide and fluoride. The depth-profiling X-ray photoelectron spectroscopy and transmission electron microscope studies illustrate that Mn-O species are deposited in the earlier period of storage, whereas the Mn-F compounds (MnF2) in the later stage. Due to the deposition of highly resistive MnF2 phase, the electrode stored for a longer period of time shows a severe cell polarization and capacity loss. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.003203jes] All rights reserved.