Evaluation of electrochemical performances of ZnFe₂O₄/γ-Fe₂O₃ nanoparticles prepared by laser pyrolysis

A ZnFe₂O₄/γ-Fe₂O₃ nanocomposite (theoretical specific capacity: 1002 mA h g^-1) was successfully synthesized by laser pyrolysis, a very attractive nanosynthesis technique characterized by high versatility and flexibility. The obtained nanopowder was thoroughly characterized by XRD, XPS, Mössbauer spectroscopy and HRTEM, which confirmed the presence of two phases. A bimodal size distribution with small particles (tens of nanometers) and large ones (above 500 nm) was revealed by SEM and TEM. The ZnFe₂O₄/Fe₂O₃ nanocomposite was tested as a negative electrode material for lithium-ion batteries, showing significantly improved lithium storage properties with a high reversible capacity and rate capability compared to a pure ZnFe₂O₄ electrode. A capacity exceeding 1200 mA h g^-1 is sustained after 100 cycles at 100 mA g^-1, with a gradual increase of the capacity during cycling. At 500 mA g^-1 current rate, a reversible and stable capacity of 360 mA h g^-1 is observed after 300 cycles. Electrochemical measurements with several electrolytes and electrode formulations were also conducted in order to explore the origin of the extra capacity and its increase with cycling.