Template-assisted loading of Fe3O4 nanoparticles inside hollow carbon “rooms” to achieve high volumetric lithium storage

The design of simultaneously high compacted density, developed porosity, and structural stability electrode materials has always been a challenge to meet the demand of high volumetric performance lithium ion storage devices. In this paper, we demonstrate a new compositing method for hollow carbon “room” loading Fe3O4 nanoparticles (HCR@Fe3O4) with the assist of Na2CO3 salt crystal templates. The as-obtained HCR@Fe3O4 composites has a massive compact density (1.79 g cm-3), abundant multimodal pores (1.26 cm3 g-1), and a large content of Fe3O4 (64.2 wt%), which leads to excellent volumetric capacitive performance. More importantly, the unique compositing model not only provides fast transmission channel for Li+, but also alleviates the mechanical strain efficiently by the cavity between the Fe3O4 nanoparticles and carbon wall. When evaluated as an anode of lithium ion batteries, the resultant HCR@Fe3O4 electrode exhibits remarkable volumetric capacity of 2044 mAh cm-3 at 0.2 A g-1, and stable cycle life of 828 mAh cm-3 after 1000 cycles at 5 A g-1. The assembled HCR@Fe3O4//AC lithium ion hybrid capacitor device exhibits a high energy density of 173 Wh L-1 at a power density of 190 W L-1, demonstrating its high-level integrated volumetric density/power density.