Evolution of a solid electrolyte interphase enabled by FeNX/C catalysts for sodium-ion storage

Abstract

The structure and chemical engineering of a solid electrolyte interphase (SEI) play a vital role in rechargeable batteries. The underlying correlation between the properties of the enhanced sodium (Na) ion storage and SEIs in metal–nitrogen (MN_X) platform electrodes was not revealed during charging and discharging cycles. Herein, the capacity enhancement of FeN_X/C anodes was first clarified by employing in situ temperature-dependent Nyquist plots and ex situ X-ray photoelectron spectroscopy. It was evidenced that physiochemical evolution of the SEI and surface carbonaceous materials made a significant contribution to the improved sodium storage performance through the following three mechanisms: (1) FeN_X catalyzed the reversible conversion of SEIs, beneficial to the storage and release of extra Na ions, (2) a large number of spin-polarized charges were stored on the surface of the reduced Fe species, and (3) the carbon delivered additional capacity through the surface-capacitive effects. As a result, the FeN_X/C anode provided a high capacity of 217 mA h g⁻¹ after 1000 cycles at 2000 mA g⁻¹. Therefore, the FeN_X species catalyzed the reversible conversion reaction of SEIs, which contributed novel avenues to the design of conversion-type electrode materials.