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The physical and electrochemical properties of LixMnO2 and LixTi0.11Mn0.89O2 synthesized from precursors made by glycine-nitrate combustion (GNC) and solid-state synthesis methods (SS) are examined in this paper. The highest specific capacities in lithium cells are obtained for SS-LixMnO2 electrodes at low current densities, but GNC-LixTi0.11Mn0.89O2 electrodes show the best high rate performance. These results can be explained by changes in the voltage characteristics and differences in the particle morphologies induced by the Ti-substitution and synthesis method. Ti-substitution also results in a decrease in the electronic conductivity, but greatly improves the thermal properties and imparts dissolution resistance to the electrode. For these reasons, it is preferable to use LixTi0.11MnO0.89O2 in lithium battery configurations rather than LixMnO2. Suggestions for improving the electrochemical performance of the Ti-substituted variant are given based on the results described herein.

This work demonstrates the protective effect of partial titanium substitution in LixTi0.11 Mn0.89O2 against surface decomposition in room-temperature ionic liquid (RTILs) cells. Raman microscopy and reflectance Fourier transform IR (FUR) spectroscopy were used to analyze electrodes recovered from cycled Li/LixTiyMn1-yO2 (y = 0, 0.11) cells containing the 0.5 mol/kg LiTFSI in P13FSI RTIL electrolyte. [TFSI = bis(trifluoromethanesulfonyl)imide.] Raman and FTIR spectra of cycled LixMnO2 cathodes showed many distinct bands that can be attributed to both the electrolyte and electrode decomposition products. The thickness of the amorphous porous layer on the LixMnO2 cathode increased during cycling. The surface degradation of LixMnO2 and precipitation of electrolyte decomposition products contributed to the film growth. Improved cycling behavior was observed in cells containing LixTi0.11 Mn0.89O2, yet Raman spectroscopy also showed possible surface degradation. The FTIR spectra of cycled LixMnO2 and LixTi0.11Mn0.89O2 cathodes displayed bands characteristic for LiSO3CF3 and Li2NSO2CF3, which originate from the reaction of the TFSI anion with traces of water present in the cell. [ABSTRACT FROM AUTHOR]

Abstract: Computational and experimental work directed at exploring the electrochemical properties of tetrahedrally coordinated Mn in the +5 oxidation state is presented. Specific capacities of nearly 700mAhg−1 are predicted for the redox processes of Li x MnO4 complexes based on two two-phase reactions. One is topotactic extraction of Li from Li3MnO4 to form LiMnO4 and the second is topotactic insertion of Li into Li3MnO4 to form Li5MnO4. In the experiments, it is found that the redox behavior of Li3MnO4 is complicated by disproportionation of Mn5+ in solution to form Mn4+ and Mn7+ and by other irreversible processes; although an initial capacity of about 275mAhg−1 in lithium cells was achieved. Strategies based on structural considerations to improve the electrochemical properties of MnO4 n− complexes are given. [Copyright &y& Elsevier]