Li-Ion Capacitors Based on Activated Ferric Oxide as an Anode

Low-cost Fe-based electrode materials for Li-ion energy storage devices attract lots of attention. In this work, porous Fe₂O₃ nanoparticles are synthesized by a simple route. First, their lithium storage performance is investigated by assembling half-cell configurations with Li foil as the counter electrode. During initial dozens of cycles, capacities of Fe₂O₃ nanoparticles fall off rapidly, which is related to continuous growth of solid electrolyte interphase (SEI). Amazingly, the capacities show an upturn in extended cycles. The pseudocapacitance of activated capacities is revealed by executing cyclic voltammetry (CV) tests at various scan rates on 500-cycled Fe₂O₃ electrodes. Based on electrochemical results, we speculate this special cycling performance of Fe₂O₃ nanoparticles may be associated with reversible electrochemical processes of SEI under the catalysis of nano-size Fe. Further, 500-cycled Fe₂O₃ anodes are reassembled with activated carbon cathodes for Li-ion capacitors (LICs). The LICs show energy densities of 110 Wh kg⁻¹ at power densities of 136 W kg⁻¹, and 72.8% capacity retention after 3000 cycles at 2 A g⁻¹. We report an interesting electrochemical behavior of porous Fe₂O₃ nanoparticles, and a high-performance LIC based on activated Fe₂O₃ as an anode. This work may offer a new understanding for lithium storage capacities of metal oxide anodes.