Close-packing of hierarchically structured C@Sn@C nanofibers for high-performance Li-ion battery with large gravimetric and volumetric energy densities

The fabrication of nanostructure can alleviate the problem of electrode pulverization so as to exhibit high cycling stability with large gravimetric energy density. However, the high volumetric fraction of voids in nanomaterials inevitably results in low tap density and poor volumetric energy density. Herein, we prepared micron-sized hierarchical fibrous bundle that is composed of [email protected]@C nanofibers with close-packing arrangement. The [email protected]@C primary nanofiber provided efficient structural accommodation to the huge volumetric change, showing high cycling stability with large gravimetric energy density. The close-packing of constituent [email protected]@C nanofibers minimizes the voids and porosity of formed micron-sized fibrous bundle, exhibiting an extremely high tap density of 1.31 g cm−3, superior to the sandwiched [email protected]@C nanofiber (0.53 g cm−3) and [email protected]@C microfiber (0.94 g cm−3) without close-packing arrangement. At the current density of 0.5 A g−1, the gravimetric energy density of [email protected]@C nanofiber bundle still reached ∼ 580 mAh g−1, with corresponding volumetric energy density of ∼ 760 mAh cm−3, higher than those of [email protected]@C and [email protected]@C by ∼ 437 and ∼ 210 mAh cm−3, respectively. Notably, the gravimetric energy density of [email protected]@C nanofiber bundle is superior to most transition-metal oxides, and the volumetric energy density is comparable to high-performance Si anodes.