Low-temperature synthesis of alpha-MnO2 hollow urchins and their application in rechargeable Li+ batteries.

Novel alpha-MnO2 hollow urchins were synthesized on a large scale by a facile and efficient low-temperature (60 degrees C) mild reduction route, without templates or surfactants in the system. The formation mechanism for the hollow urchins was proved to be the Ostwald ripening process by tracking the crystallization and morphology of the product at different reaction stages. The as-prepared hollow-urchin sample has a high Brunauer-Emmett-Teller surface area of 132 m(2)/g and a mesoporous structure, which were expected to help improve the electrochemical property in Li+ batteries. When the alpha-MnO2 hollow urchins were used as the cathode material in Li batteries, they performed better than the other alpha-MnO2 samples (solid urchins and dispersed nanorods), indicating that the electrochemical performance of the electrode material is sensitive to its morphology. This synthetic procedure is straightforward and inexpensive and thus facilitates mass production of alpha-MnO2 hollow urchins.