Crystallization of MnO2 by Microwave-Hydrothermal Synthesis and Its Applications for Supercapacitors and Lithium-Ion Batteries

MnO2 with different crystal phases, beta- and gamma-MnO2 and various morphologies, rod-, wire-, and plate-like structures, have been crystallized by microwave-hydrothermal method. Time dependent studies reveal that the shapes and phases of MnO2 can be transformed from wire- and plate-like structured gamma-MnO2 to rod- like structured beta-MnO2. In addition, the crystal phases and morphologies can be controlled by finely adjusting the reaction temperatures and times. The microwave-hydrothermally synthesized MnO2 were investigated as potential electrode materials for supercapacitors and lithium ion battery cathodes. Low reaction temperature and short reaction time can improve the electrochemical performances of MnO2. The present results prove that gamma-MnO2 with 1 x 2 tunnel-structures have higher electrochemical performances than that of beta-MnO2 with 1 x 1 tunnels. The crystallization of MnO2 with proper structures and morphologies can achieve better performance in their applications.