Magnetically Aligned Tetragonal FeS as Anode for Improved Rate Capability in Sodium Ion Batteries

The capacity and rate capabilities are profoundly related to the geometric configuration of the active material in electrodes; however, this effect has not been extensively studied in SIBs because of the complexity of the multicomponent mixed system. Here, this correlation is demonstrated using an oriented 2D tetragonal FeS nanoflake model system for SIBs. An external magnetic field-induced facile method for macroscopic alignment critically improves porosity and tortuosity. The effects of these differences on the capacity vary depending on the current density. Porosity is influential over a wide range of current densities, whereas tortuosity becomes significant near a rate of 1 C. The magnetic alignment along the out-of-plane direction leads to higher porosity and lower tortuosity, noticeably improving the capacity by 90% compared to that of the in-plane-aligned anode at 1 C.