A new strategy for achieving a high performance anode for lithium ion batteries-encapsulating germanium nanoparticles in carbon nanoboxes

A novel strategy to improve the electrochemical performance of a germanium anode is proposed via encapsulating germanium nanoparticles in carbon nanoboxes by carbon coating the precursor, germanium dioxide cubes, and then subjecting them to a reduction treatment. The complete and robust carbon boxes are shown to not only provide extra void space for the expansion of germanium nanoparticles after lithium insertion but also offer a large reactive area and reduced distance for the lithium diffusion. Furthermore, the thus-obtained composite, composed of densely stacked carbon nanoboxes encapsulating germanium nanoparticles (germanium at carbon cubes (Ge at CC)), exhibits a high tap density and improved electronic conductivity. Compared to carbon-coated germanium bulks, the Ge at CC material shows excellent electrochemical properties in terms of both rate capability and cycling stability, due to the unique cubic core-shell structure and the effective carbon coating, so that the Ge at CC electrode delivers ≈497 mA h g-1 at a current rate of 30 C and shows excellent cycling stability of 1065.2 mA h g-1 at 0.5 C for over 500 cycles.