Free standing Si (Ge) nanowire/Cu nanowire composites as lithium ion battery anodes

Abstract

Silicon (Si) and germanium (Ge) can alloy with lithium to achieve high theoretical specific capacities (3579 mAh/g for Li15Si4 and 1384 mAh/g for Li15Ge4), which are several times greater than commercial graphite (372 mAh/g). However, they exhibit significant volume and crystal structural change during cycling processes, leading to structural pulverization and loss of electrical conduction paths between individual active materials and current collector. We report a non-carbon based free standing electrodes fabricated by directly mixing Si and Ge nanowires with Cu nanowires as lithium ion battery anodes. The one dimensional nanostructure of Si (Ge) and Cu provide good charge transport along their length and many contact points were formed between NWs after annealing process. The nanowire composites have several advantages compared to the conventional electrode that slurry materials are coated on a metal foil. For example, the weight is lighter than conventional electrodes because it does not need a current collector and is fabricated without any additives, and binders. Moreover, the space among the nanowires can accommodate the volume contraction of Si (Ge) during alloying and dealloying process and enhance the electrolyte penetration.