Template-free synthesis of hollow Li2O–Fe2O3–Ag heterostructures for ultra-high performance Li-ion batteries

Abstract

A carbon-free, three-dimensional hollow hybrid structure has been synthesized by a facile template free hydrothermal method and used as an ultra-high performance Li-ion battery anode. The heterostructure is composed of Fe₂O₃, Li₂O and Ag, where the high theoretical capacity of Fe₂O₃ has been fully exploited by incorporating Ag and Li₂O into the system. This strategy allows a strong synergistic effect leading to high reversible capacity, exceptional cycling stability and excellent rate capability. The addition of Li₂O enhances the electrochemical performance of Fe₂O₃ by prohibiting its agglomeration. It further acts as an oxidant facilitating the recovery of Fe to Fe₂O₃ during the charge step and as a buffer matrix which effectively cushions the volumetric stresses generated during cycling. The addition of Ag aids in suppressing the irreversible capacity loss, improves the electrical conductivity and adds to the capacity via Li alloying. This smart hybrid composition coupled with a special hollow structure allows the heterostructure to deliver high initial coulombic efficiency (∼86%) and high reversible capacity (∼1350 mA h g⁻¹ at 100 mA g⁻¹) with almost no capacity fading. Furthermore it demonstrates an excellent rate performance delivering capacities of ∼950, 780 and 610 mA h g⁻¹ at high current rates of 0.5, 1 and 2 A g⁻¹.