Nano-GeTe Embedded in a Three-Dimensional Carbon Sponge for Flexible Li-Ion and Na-Ion Battery Anodes

Among the germanium-based compounds, GeTe is a promising anode candidate that exhibits high theoretical capacity (856 mAh g^-1 vs Li⁺/Li and 401 mAh g^-1 vs Na⁺/Na) and low volume expansion during an ion intercalation/deintercalation process. Nevertheless, achieving good dispersion of metal-like GeTe in anode materials remains a significant challenge. Herein, hybrid GeTe/graphene (GeTe/G) is proposed as a highly efficient anode for LiBs and SiBs by facile ball milling. Pulverized GeTe is effectively anchored on peeled graphene sheets that can accelerate Li⁺ transport in electrodes as predicted by theoretical calculations and thus result in improved overall electrochemical performance. For instance, GeTe/G possesses a high reversible capacity of 478 mAh g^-1 under 0.1 A g^-1 in the 300th cycle. Moreover, by further cross-linking the GeTe/G using carbon nanotube (CNT) and carbon nanofiber pyrolysis from cotton cellulose, the as-prepared three-dimensional (3D) flexible anode possesses macropores that acted as positive channels favorably for ion transport. Remarkably, the as-prepared flexible 3D GeTe/G/CNT electrode with a thickness of 1050 μm exhibits a high reversible capacity of 451.4 mAh g^-1 (4.38 mAh cm^-2) vs Li⁺/Li and 372.5 mAh g^-1 (2.08 mAh cm^-2) vs Na⁺/Na, respectively, in the second cycle under 0.1 A g^-1. These results shed some light on the direct application of 3D flexible carbon sponge electrodes in high-performance LiBs/SiBs.