Hydrothermal Synthesis of Manganese Dioxide Nanoparticles as Cathode Material for Rechargeable Batteries

Rod-shaped manganese dioxide (MnO2) nanoparticles with three different crystallographic phases, namely alpha-, beta-, and gamma-MnO2, were hydrothermally prepared. The products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Brunaure-Emmett-Teller (BET) method, and electrochemical measurements as cathode materials for secondary lithium-ion batteries. The crystalline phase of MnO2 depended mainly on the Mn concentration of precursor solution and reaction temperature whereas it was not influenced by the pH value of precursor solution. All the samples were obtained as secondary particles composed of rod-shaped nanoparticles and the sizes of alpha- and gamma-MnO2 were smaller than that of beta-MnO2. In electrochemical tests, the gamma-MnO2 had the highest initial capacity of 190 mA h g(-1) among three different crystal phases and maintained better performance than the other crystallographic samples in the subsequent discharge/charge cycles. As a result, the electrochemical performance of MnO2 depends on the crystal structure rather than the particle size. (c) The Electrochemical Society of Japan, All rights reserved.