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

The design of electrodes with simultaneously high compaction density, developed porosity, and structural stability has always been a challenge so as 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 of Fe3O4 nanoparticles (HCR@Fe3O4) with the assistance of Na2CO3 salt crystal templates. The as-obtained HCR@Fe3O4 composites have a massive compaction 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 a fast transmission channel for Li+ but also alleviates the mechanical strain efficiently through the cavity between the Fe3O4 nanoparticles and the carbon wall. When evaluated as an anode of lithium ion batteries, the resultant HCR@Fe3O4 electrode exhibits a remarkable volumetric capacity of 2044 mA h cm−3 at 0.2 A g−1 and a stable cycle life of 828 mA h 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 W h L−1 at a power density of 190 W L−1, demonstrating its high-level integrated volumetric density/power density.