Amorphous Hierarchical Porous GeOx/Reduced Graphene Oxide Composite As a High-Performance Anode Material for Lithium Ion Batteries

Abstract

The conventional graphite anode is still insufficient to meet the demand due to its low theoretical specific capacity(372 mAhg-1). Compared to the graphite, the high surface-to-volume ratio and open porous system of graphene shows great advantages:i) fast ion transport enabling the high rate capability, which is an obstacle for graphite with microsize bulk lithium diffusion; ii) the large surface areas of graphene can provide more electrochemical reaction active sites for energy storage. Meanwhile, Graphene is an excellent substrate to host active nanomaterial for energy applications due to its high conductivity, large surface area, structural flexibility, and chemical stability.1,2Overall, the superior electronic conductivity and mechanical properties of graphene make it suitable for fabrication into high-performance composites with other anode materials for LIBs. Recently, Alloy-type anodes (Si, Ge, Sn, Sb, etc.) have attracted much attention due to their higher Li storage capacity than the graphite anode that is currently used in Li-ion batteries. Compared with the silicon etc., Germanium has high theoretical capacity (1384 mAh/g), good lithium diffusivity (400 times faster than in silicon), and high electrical conductivity (104 times higher than silicon).3 However, the practical usage of Ge as an anode material is hindered by dramatic volume changes (∼300%) caused by insertion/extraction of lithium ions, which results in crack and pulverization, and loss of electrode contact.4 Herein, we developed a facile synthesis method (solution-phase reactions) to form hybrid materials of amorphous hierarchical porous GeOx whose primary particles are 3∼7 nm diameter anchored on reduced grapheme oxide (RGO) sheets for lithium ion battery applications. The high rate performance of mesoporous GeOx/RGO composite is attributed to (1) the amorphous hierarchical porous GeOx whose primary particles are 3∼7 nm diameter anchored on conducting RGO stabilize the cycling performance and rate capability; (2)fast charge transfer reaction at the large interfacial area of RGO between hybrid electrode and liquid electrolyte. Acknowledgements This work is supported by the Project of the Ningbo 3315 International Team of Advanced Energy Storage Materials, China Postdoctoral Science Foundation funded project.