Iron Oxide Nanosheets As High Performance Cathodes for Lithium-Ion and Sodium-Ion Batteries

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Cathodes with high lithium-ion and sodium-ion capacities, the ability to be rapidly charged and discharged, and that are extremely low-cost are needed for numerous applications including electric vehicles, consumer devices, and grid-level energy storage. Iron oxides are of significant interest based on their low cost, low toxicity, and high natural abundance, however iron oxide cathodes typically have low specific capacities and very poor rate capabilities. Our work has shown that synthesizing and stabilizing iron oxide in a nanosheet architecture results in significantly improved lithium-ion charge storage capacities compared to iron oxide nanoparticles at both slow and fast charging/discharging times. The iron oxide nanosheets were determined to have lateral dimensions of ~50 nm, thicknesses of ~1 nm, and be composed of smaller crystallites. From X-ray diffraction, Raman spectroscopy, and high resolution microscopy, the structure of the nanosheets was consistent with maghemite, γ-Fe2O3. The γ-Fe2O3 nanosheets exhibit significantly better electrochemical properties with higher capacities and rate capabilities (110 mAh/g at ~3C) compared with comparable iron oxide nanoparticles. The improved electrochemical performance of γ-Fe2O3 nanosheets has been demonstrated to be related to multiple factors including high surface area, a predominantly surface charge storage process, and higher electronic conductivity. Our recent work has explored using γ-Fe2O3 nanosheets for sodium-ion battery cathodes. The understanding of the unique electrochemical properties, factors that stabilize the nanosheet form, and distinct charge storage mechanism of iron oxide nanosheets furthers the design of improved charge storage materials with improved capacities, rate capabilities, and lower cost.