Pseudocapacitive vs diffusion controlled charge storage in Fe2O3 nanosheet Na-ion battery

Abstract

Despite of its high potential to be the inexpensive-sustainable replacement to lithium, practical deployment of the sodium ion batteries has been practically hindered by the lack of high performance affordable anodes. The practical use of hematite (Fe2O3) electrodes, a high capacity-earth abundant conversion type Na-ion compatible anode, is practically limited by its substantial volumetric fluctuation upon de/sodiation and constraint electronic transport. Herein, we demonstrate highly reliable pseudocapacitive type Fe2O3 nanosheet anodes for Na-ion batteries produced using a simple but largely industrially viable approach. A unique combination of two dimensional morphology and the optimum crystal perturbations collectively impart an exceptional charge transport characteristics and substancial volume fluctuation buffering. Owing to the distinct 2D morphology and structural features, this nanosheet electrode exhibited dominant pseudocapacitive nature with a maximum contribution of 95 % and delivered good reversible specific capacity and cyclability. Mechanistic investigations with the in-situ Raman analysis revealed insignificant structural changes indicating pseudocapacitive nature of the conversion reaction facilitated by the diffusion independent fast Na-ion mobility in the host lattice. The demonstrated method of producing transition metal oxide electrodes with good commercialization potential may be further exploited to achieve the goal for high performance-sustainable batteries.