In situ quantization of ferroferric oxide embedded in 3D microcarbon for ultrahigh performance sodium-ion batteries

Abstract

Unlike conventional carbon coating strategies which only focus on the macrodimension to enhance electrical conductivity and alleviate volume variation for high-capacity metal oxide anode materials, a hierarchically raspberry-like microstructure embedded with three-dimensional carbon-coated Fe₃O₄ quantum dots is built for ultrafast rechargeable sodium ion batteries. Taking advantage of using metal organic frameworks (MOFs) as templates, it realizes an in situ quantization process in which Fe₃O₄ quantum dots are formed and uniformly embedded in microcarbon coating protection. Due to the short diffusion length and integrated hierarchical conductive network, the electrode combines supercapacitor-like rate performance (e.g., less than 6 minutes to full charge/discharge) and battery-like capacity (e.g., maintaining >90% of theoretical capacity). An interesting surface-induced process which imitates pseudocapacitive behaviors in supercapacitors is analyzed in detail. This proof-of-concept study and insightful understanding on sodium storage in this investigation may inherently solve the widely encountered problems existing in high-capacity metal oxide anode materials and point out new directions for the future development of ultrafast rechargeable sodium ion batteries.