Honeycomb-like Macro-Germanium as High-Capacity Anodes for Lithium-Ion Batteries with Good Cycling and Rate Performance

Abstract

Macro-Ge powder has been synthesized with a novel hydrothermal reduction of commercial GeO2 at 200 °C in an autoclave. The obtained macro-Ge product demonstrates a honeycomb-like macroscopic network structure with a high tap density of 2.19 g cm–3. As for the anode material of lithium ion batteries, the macro-Ge electrode exhibits 1350 mAh g–1 at the current rate of 0.2 C and with 64% capacity retention over 3500 total cycles at 1 C. The macro-Ge contains a honeycomb porous structure, which allows for a high volumetric capacity (∼3000 mAh cm–3). Moreover, the symmetrical and asymmetric rate behaviors also provide its excellent electrochemical property. For example, the macro-Ge electrode can be rapidly charged to 1130 mAh g–1 in 3 min (20 C) and 890 mAh g–1 in 90 s (40 C) using the constant discharge mode of 1 C. Furthermore, the Ge electrode still maintains over 1020 mAh g–1 at 1 C for 300 cycles at the high temperature (55 °C) environment. When coupled with a commercial LiCoO2 cathode, a 3.5 V lithium-i...