Wednesday, 31 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
As an anode material, germanium dioxide (GeO2) has a high theoretical capacity of 2152 mAh/g, considering its sequential conversion and alloying reactions. However, the development of stable GeO2 anodes has been hindered by a large volume change during Li-ion insertion/extraction and irreversible conversion reaction of GeO2 from Ge metal state. In this presentation, we present the synthesis of nanoporous composite materials (m-GeO2, m-GeO2-C and m-Ge-GeO2-C) with large mesopore size, developed by a block copolymer (BCP) directed self-assembly approach. Among the samples, m-Ge-GeO2-C exhibited greatly improved reversible capacity (1631 mAh/g), high coulombic efficiency, and stable cycle-life, compared with the other control electrodes. The enhanced performance is attributed by the highly improved conversion reaction due to the synergistic effects of the nanoporous (buffer volume for relieving the structural stress) and the composite structures (enhanced reversibility). The direct evidence for reversible conversion reaction of GeO2 are studied by electrochemical evaluation, ex-situ X-ray diffraction (XRD), and in-situ X-ray absorption spectroscopy (XAS). We show that the tailoring nanostructures and composition of GeO2 can significantly enhance their electrochemical performance.