Hollow Fe3O4 spheres as functional architectures for advanced Li–O2 batteries

Although the catalyst intrinsic catalytic activity is crucial for enhancing the performance of Li–O2 batteries, its morphology also plays a significant role. Bulk catalysts often show limited catalytic efficiency, likely due to their large particle size and low specific surface area. As is well known, highly efficient catalysts require high surface area and a greater number of active sites. In this frame, this work reports the use of Fe3O4 hollow spheres obtained through ALD deposition technique onto sacrificial PVP nanoparticles as catalyst for Li–O2 batteries. Rotating disk electrode studies show the catalyst ability to shift the oxygen reduction reaction (ORR) from a 2 to a 2 + 2 electrons mechanism. Further studies in classical Li–O2 cell set-up using DMSO with LiTFSI 0.5 M as liquid electrolyte, indicate that the catalyst allows to modify the Li2O2 formation pathway upon discharge, from solution to surface growth. This results in higher reversibility and slower DMSO degradation upon cycling visible through a larger full cell capacity (5.9 against 5.1 mAh cm-2 for a standard cell), but above all an almost three-fold increase of the cycle life (from 45 to 130 cycles, corresponding to approximately 1300 h of operation) at 0.1 mA cm-2 and at the curtailed capacity of 0.5 mAh cm-2.