Scalable Solution-Grown High-Germanium-Nanoparticle-Loading Graphene Nanocomposites as High-Performance Lithium-Ion Battery Electrodes: An Example of a Graphene-Based Platform toward Practical Full-Cell Applications

Graphene in the form of graphene/nanocrystal nanocomposites can improve the electrochemical performance of nanocrystals for lithium-ion (Li-ion) battery anodes, which is especially important for high-capacity Li-alloy materials such as Si and Ge. For practical full-cell applications, graphene composite electrodes consisting of a large portion of active materials (i.e., a surface of graphene sheets evenly distributed with dense nanoparticles) are required. We have developed a facile solution-based method to synthesize subgram quantities of nanocomposites composed of reduced graphene oxide (RGO) sheets covered with a high concentration (similar to 80 wt %) of single-crystal 4.90(+/- 0.80) nm diameter Ge nanoparticles. Subsequently, carbon-coated Ge nanoparticles/RGO (Ge/RGO/C) sandwich structures were formed via a carbonization process. The high-nanoparticle-loading nanocomposites exhibited superior Li-ion battery anode performance when examined with a series of comprehensive tests, such as receiving a practical capacity of Ge (1332 mAh/g) close (96.2%) to its theoretical value (1384 mAh/g) when cycled at a 0.2 C rate and having a high-rate capability over hundreds of cycles. Furthermore, the performance of the full cells assembled using a Ge/RGO/C anode and an LiCoO2 cathode were evaluated. The cells were able to power a wide range of electronic devices, including an light-emitting-diode (LED) array consisting of over 150 bulbs, blue LED arrays, a scrolling LED marquee, and an electric fan. Thus, this study demonstrates a proof of concept of the use of graphene-based nanocomposites toward practical Li-ion battery applications.