Preparation of iron oxide/carbon composite electrode of Li-ion battery by using lipid-extracted microalgae as a template

Abstract

In order to prevent future problems regarding depletion of fossil fuels, lithium-ion battery has arisen as a reliable energy supply system that can fulfill practical usage of electric vehicles. However, with the limited energy storage capacity of graphite anode materials (372 mAh $g^{-1}$) in conventional lithium-ion batteries, scientists have conducted on alternative anode materials in the interest of high energy storage capacity. Among those materials, $Fe_3O_4$ has been considered as promising candidate of anode materials because of its high theoretical capacity (982 mAh $g^{-1}$). However, large amount of lithium-ion storage leads to the short cycle life, which is caused by severe volume change during the charge/discharge reaction. There have been many studies to solve this problem. In particular, it was confirmed that active material/carbon composite materials exhibit much enhanced cycle retention. This is attributed to the carbon matrices that alleviate the volume expansion. This research aimed to verify the effectiveness of using microalgae that can provide carbon matrices as a biotemplate. Spray drying was implemented to synthesize hollow spherical primary particles. In six different conditions, the primary particles were heat treated to be synthesized into iron oxide/carbon composites. From these composites’ characterization through XRD and TGA, $Fe_3O_4$/Carbon composite electrode was synthesized in optimized heat treatment conditions. The electrochemical performance of optimized composite was compared with other composites. Finally, the $Fe_3O_4$/Carbon composite was further analyzed with BET & pore size, TEM, and FIB-SEM. $Fe_3O_4$/Carbon composite electrode had the reversible capacity of 1231 mAh $g^{-1}$ whereas carbon template removed composite only showed 249 mAh $g^{-1}$ after 300cycles at current density of 400 mA $g^{-1}$.