Fábio A. Amaral

Characterization and electrochemical performance of the spinel LiMn2O4 prepared from ε-MnO2

Abstract The preparation and characterization of the spinel LiMn 2 O 4 obtained by solid state reaction from quasi-amorphous e-MnO 2 is reported. A well-defined highly pure spinel was characterized from X-ray diffractograms. The average manganese valence of e-MnO 2 and spinel samples was found to be 3.89±0.01 and 3.59±0.01, respectively. The electrochemical performance of the spinel was evaluated through cyclic voltammetry and chronopotentiometry. The voltammetric profiles obtained at 1 mV/s for the LiMn 2 O 4 electrode in 1 M LiClO 4 dissolved in a 2:1 mixture of ethylene carbonate and dimethyl carbonate showed typical peaks for the lithium insertion/extraction reactions. The charge capacity of this electrode was found to be ∼110 mA h g −1 for the first charge/discharge cycles.

Produção de dióxido de manganês eletrolítico para uso em baterias de lítio

The e phase of electrolytic manganese dioxide (EMD) is the structural form most easily converted in the LiMn2O4 spinel used as cathode in lithium batteries. Thus, employing titanium as anode, a study of electrolysis parameters was carried out in order to determine the best conditions to produce an e-EMD suitable for that spinel preparation. The influence of solution temperature (65oC and 90oC) and current density (between 1 mA/cm2 and 17.5 mA/cm2) on the anode potential and the EMD properties was investigated using an aqueous 2.0 mol/L MnSO4 + 0.30 mol/L H2SO4 solution. In any of the electrolysis conditions tested only the e-EMD structure was obtained, but its specific surface area varied with the applied current density and temperature. Drying the e-EMD at temperatures between 60oC and 120oC did not cause any phase changes. To produce a suitable EMD at the highest current density possible without passivation of the titanium anode, the best electrolysis parameters were determined to be 90oC and 15 mA/cm2. The e-EMD thus obtained had a specific surface area (BET) of ca. 65 m2/g.

New Synthesis Method for a Core-Shell Composite Based on α-Bi2O3@PPy and its Electrochemical Behavior as Supercapacitor Electrode

New composite based on polypyrrole (PPy) and bismuth oxide (α-Bi2O3) was investigated as supercapacitor electrode. The α-Bi2O3 was obtained by hydrothermal route at 500 C for 2 h. Cyclic voltammetry was used to electropolymerize PPy on graphite electrode (GE) or on GE/α-Bi2O3. The X-ray diffraction profile of Bi2O3 revealed the α-Bi2O3 monoclinic structure with space group P21/c. The scanning and transmission electron microscopy images showed that PPy coated α-Bi2O3. Raman spectra showed that PPy inhomogeneously coated α-Bi2O3, but it was still possible to obtain a α-Bi2O3@PPy core-shell hybrid composite with highly ordered α-Bi2O3 with electronic interaction between the oxide and the polymer chain of the polymer. The GE/α-Bi2O3@PPy composite electrode (type I supercapacitor) displayed a predominantly capacitive profile with low impedance values and good electrochemical stability after 50 charge and discharge cycles. The specific capacitance of α-Bi2O3@PPy composite was found in the range of 634 to 301 F g to gravimetric current of 3 and 10 A g, respectively.