Heterolayered Li+-MnO2-[Mn1/3Co1/3Ni1/3]O2 Nanocomposites with Improved Electrode Functionality: Effects of Heat Treatment and Layer Doping on the Electrode Performance of Reassembled Lithium Manganate

Novel heterolayered nanocomposites consisting of interstratified MnO2 and [Mn1/3Co1/3Ni1/3]O-2 nanosheets are synthesized by a layer-by-layer self-assembly between negatively charged metal oxide nanosheets and lithium cations. According to powder X-ray diffraction and micro-Raman analysis, all of the as-prepared Li+-xMnO(2)-(1-x)[Mn1/3Co1/3Ni1/3]O-2 nanocomposites with x = 1, 0.7, and 0.4 have a lamella structure with similar basal spacing of similar to 7.1 angstrom, indicating the formation of lithium intercalation structure with cointercalated water bilayers. The nanoscale mixing of MnO2 and [Mn1/3Co1/3Ni1/3]O-2 nanosheets is confirmed by energy-dispersive spectrometry-elemental mapping analysis. Upon a self-assembly with Li+ ions, there occur no marked changes in the octahedral symmetry and mixed oxidation state of M3+/M4+ ions (M = Mn, Co, and Ni) in the precursor metal oxide nanosheets. All of the as-prepared nanocomposites commonly experience a structural transformation from hydrated layered structure to dehydrated layered structure at 200 degrees C, which is followed by the second-phase transition to cubic spinel structure at 600 degrees C. Despite distinct structural changes of the nanocomposites at elevated temperatures, their porous stacking structure is well-maintained up to 400 degrees C. The heat-treatment at 400 degrees C leads to a significant improvement of the discharge capacity of the present nanocomposites because of the dehydration of as-prepared materials and the enhancement of crystallinity. The doping of [Mn1/3Co1/3Ni1/3]O-2 layers enables us not only to increase the discharge capacity of the Li-MnO2 nanocomposite but also to prevent the phase transition of layered manganese oxide to spinel structure during electrochemical cycling. The present study clearly demonstrates that a postcalcination process as well as a partial doping of [Mn1/3Co1/3Ni1/3]O-2 layer is effective in improving the electrode performance of reassembled Li-MnO2 nanocomposites.