Fe3O4-Based Anodes with High Conductivity and Fast Ion Diffusivity Designed for High-Energy Lithium-Ion Batteries

A nitrogen and sulfur comodified graphene-coated sea urchin-like (Fe3O4@C composite (Fe3O4@C@NS-rGO) is prepared by a hydrothermal method combined with a subsequent pyrolysis process. Using (Fe3O4@C@NS-rGO as an anode in a lithium-ion battery, its reversible capacity reaches 532.5 mAh/g at 100 mA/g after 100 cycles. The lithium-ion full battery configurated by (Fe3O4@C@NS-rGO and LiCoO2 ((Fe3O4@C@NS-rGO parallel to LiCoO2) shows a working voltage of 3.25 V and an energy density of 232.1 Wh/kg (vs cathode). For the (Fe3O4@C@NS-rGO composite, the sea urchin-like hollow structure makes it easier for the electrolyte to infiltrate, the holes can provide space for the volume change, and the one-dimensional rodlike structure around the sea urchin can shorten the transmission path of lithium ions and electrons. Moreover, the introduction of carbon and NS-rGO can increase the electron conductivity and also provide a double buffering effect on the volume change, especially heteroatom functionalization can also provide plentiful active sites for ion adsorption within the electrode, thereby giving excellent lithium-ion storage properties related to the reversible capacity, rate capability, and cycling performance. Such a concept of material design will open up a new strategy for preparing similar advanced anode materials toward high-energy storage systems.