Cobalt ferrite thin films as anode material for lithium ion batteries

Abstract

Spinel cobalt ferrite (CoFe 2O 4) thin films have been fabricated by 355 nm reactive pulsed laser deposition on stainless steel substrates. XRD and SEM analyses showed that the CoFe 2O 4 films exhibited a polycrystalline structure and were composed of nanoparticles with an average size of 80 nm. At 1C rate, the initial irreversible capacity of polycrystalline CoFe 2O 4 film electrode cycled between 0.01 and 3.0 V reached 1280 mAh/g. After 20 cycles, the reversible discharge capacities decreased and sustained about 610 mAh/g. The diffusion coefficient of Li ion for CoFe 2O 4 films was determined by ac impedance method, and the average value was estimated to be 1.1 × 10 −13 cm 2/S. Based on ex situ XRD, SEM and XPS data, the electrochemical mechanism of CoFe 2O 4 film with lithium upon cycling was proposed. During the first discharge, the amorphization process of CoFe 2O 4 film electrode is accompanied with the reduction of Co 2+ and Fe 3+ into metal Co and Fe, respectively, and then the reversible oxidation/reduction processes of Co, Fe and Li 2O take place in the subsequent charge/discharge cycles.