Iron-Based Oxides with Tunable Porosity by Organic Acid Etching as Electrode Materials for Lithium-Ion Batteries

With the global increasing demand for energy storage, developing high energy density and safe lithium-ion batteries (LIBs) is critical. Iron oxides are considered promising active materials for LIB anodes owing to their high-capacity, earth-abundance, non-toxicity, and low- flammability. However, iron oxides encounter issues such as poor ionic conductivity, low Columbic efficiency, and severe structural expansion during charge/discharge reactions, hindering their applications in LIBs.<br/><br/>Porous materials are considered potential candidates to buffer the volume variation of LIB anodes during cycling. In this work, iron-based oxides with tunable porosity are formed using a simplified and non-toxic organic acid etching process, which is then applied to anode materials for LIBs. Their electrochemical properties at electrode/electrolyte interfaces are investigated. Furthermore, the etching conditions for iron-based oxides are optimized to improve the cycle-life retention and rate-capability of LIB anodes.<br/><br/>Etched iron-based-oxide powders are mixed with carbon black (Super P), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) to form an aqueous-based electrode slurry, which is then coated onto a copper foil by doctor-blade casting to form an electrode, followed by baking in a vacuum oven. After battery assembly, galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) are conducted to analyze the cycle-life retention, Coulombic efficiency, and the impedance reduction of electrodes. Besides, the porosity of etched iron-based-oxide powders is characterized by Brunauer-Emmett-Teller (BET) surface area analyses. Field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) are conducted to analyze the morphology and composition of active materials, respectively. This work offers a novel approach to improve the retention and rate-capability of LIB anodes through etching iron-based oxides with organic acid.