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

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-ion battery with capacity retention of 91% (∼364 Wh kg^–1) over 100 cycles is achieved. These outstanding properties may be attributed to the honeycomb structure, for which the porous architectures supply the high efficient ionic transport and buffers the volume change during the lithiation/delithiation processes. Moreover, with bulk frameworks it ensures the high tap density and further improves the energy density. It is supported that the macro-Ge acts as attractive anode materials for further application in rechargeable lithium ion batteries