In SituTransmission Electron Microscopy Observation of the Conversion Mechanism of Fe₂O₃/Graphene Anode during Lithiation–Delithiation Processes

Abstract

Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe2O3/graphene in LIBs by in situ transmission electron microscopy (TEM). Upon lithiation, the Fe2O3 nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li2O layer. Single-crystalline Fe2O3 nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li2O matrix. Surprisingly, the delithiated product was not Fe2O3 but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge-discharge processes of Fe2O3 in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li2O layer. The macroscopic electrochemical performance of Fe2O3/graphene was further correlated with the microcosmic in situ TEM results.

Synthesis and Electrochemical Lithium Storage Behavior of Carbon Nanotubes Filled with Iron Sulfide Nanoparticles

“…In recent years, the in situ TEM electrochemical testing technique has been used to probe structural variations of nanoscale electrode materials with high spatial resolution during discharge/charge 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. We also constructed an electrochemical nanodevice using an Fe‐S@CNT as a working electrode for an in situ TEM experiment to examine its structural changes and to obtain direct insight into its Li‐storage mechanism.…”

In-situ TEM examination and exceptional long-term cyclic stability of ultrafine Fe3O4 nanocrystal/carbon nanofiber composite electrodes

“…Although tremendous efforts have been made towards ameliorating the electrochemical performance of iron oxide-based anodes, insightful investigations using in situ TEM are rare. Inspired by recent studies on in-situ TEM characterization of other nanostructured materials, like Si [23], SnO 2 [24], Fe 2 O 3 [25], Co 3 O 4 [26] and FeF 2 [27], we examined in real time the conversion reactions and morphological changes in Fe 3 O 4 /CNF composite electrodes during the electrochemical lithiation/delithiation cycles.…”

Ultrasound-assisted synthesis of porous Co3O4 microrods and their lithium-storage properties

“…The first one is the electrolyte decomposition and inevitable formation of a solid electrolyte interphase (SEI), which is partially irreversible. The second is a reversible redox reaction mechanism, which has been previously reported in the literature [19][20][21]. The conversion mechanism of Co 3 O 4 in LIBs can be expressed as:…”