3D Yolk-Shell Structured Si/void/rGO Free-Standing Electrode for Lithium-Ion Battery.

In this study, we have successfully prepared a free-standing Si/void/rGO yolk-shell structured electrode via the electrostatic self-assembly using protonated chitosan. When graphene oxide (GO) is dispersed in water, its carboxyl and hydroxyl groups on the surface are ionized, resulting in the high electronegativity of GO. Meanwhile, chitosan monomer contains -NH2 and -OH groups, forming highly electropositive protonated chitosan in acidic medium. During the electrostatic interaction between GO and chitosan, which results in a rapid coagulation phenomenon, Si/SiO2 nanoparticles dispersed in GO can be uniformly encapsulated between GO sheets. The free-standing Si/void/rGO film can be obtained by freeze-drying, high-pressure compression, thermal reduction and HF etching technology. Our investigation shows that after 200 charge/discharge cycles at the current density of 200 mA·g-1, the specific discharge capacity of the free-standing electrode remains at 1129.2 mAh·g-1. When the current density is increased to 4000 mA·g-1, the electrode still has a specific capacity of 469.2 mAh·g-1, showing good rate performance. This free-standing electrode with a yolk-shell structure shows potential applications in the field of flexible lithium-ion batteries.