Atomic Resolution Study of Reversible Conversion Reaction in Metal Oxide Electrodes for Lithium-Ion Battery

Abstract

Electrode materials based on conversion reactions with lithium ions have shown much higher energy density than those based on intercalation reactions. Here, nanocubes of a typical metal oxide (Co3O4) were grown on few-layer graphene, and their electrochemical lithiation and delithiation were investigated at atomic resolution by in situ transmission electron microscopy to reveal the mechanism of the reversible conversion reaction. During lithiation, a lithium-inserted Co3O4 phase and a phase consisting of nanosized Co-Li-O clusters are identified as the intermediate products prior to the subsequent formation of Li2O crystals. In delithiation, the reduced metal nanoparticles form a network and breakdown into even smaller clusters that act as catalysts to prompt reduction of Li2O, and CoO nanoparticles are identified as the product of the deconversion reaction. Such direct real-space, real-time atomic-scale observations shed light on the phenomena and mechanisms in reaction-based electrochemical energy conversion and provide impetus for further development in electrochemical charge storage devices.

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

“…The initial capacity was higher than the simple sum, about 730 mA h g À 1 , contributed by each of the active constituents, and the possible reasons are described as follows. (i) The synergetic effect between the CNFs and the ultrafine Fe 3 O 4 particles that are uniformly dispersed and fully encapsulated by the carbon matrix may help improve the capacity, as demonstrated in different metal oxide/graphene composite electrodes [38,39]; and (ii) the metallic Fe formed after discharge can promote reversible formation/dissolution of SEI components consisting of various inorganic and organic compounds, which contributes extra capacities as noted previously [19,26]. In the following two cycles, however, the performance became very stable with high capacities of 840 and 828 mA h g À 1 , confirming excellent reversibility.…”

“…4f) presents crystal fringes with a spacing of 0.266 nm, corresponding to the (111) plane of Li 2 O. Li 2 O is a typical reaction product arising from the lithiation of metal oxides, like Fe 2 O 3 [25] and Co 3 O 4 [26]. The Li 2 O formed initially by the above reaction likely functioned as preferential substrates for further growth on the surface of the electrode [25,26]. The same was not reported for the in-situ lithiated Si/CNT composite [45].…”

“…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.…”

Atomic Layer‐by‐Layer Co3O4/Graphene Composite for High Performance Lithium‐Ion Batteries

“…The fi rst cycle voltammogram features a shoulder peak at 1.10 V, attributed to the reduction of Co 3+ to Co 2+ , and the main cathodic peak at 0.85 V is related to the reduction of Co 2+ to Co and the formation of the solid electrolyte interphase (SEI) fi lm. [ 13 ] The anodic peak at 2.06 V represents the oxidation of Co to CoO. In the following cycles, the ATMCNs-GE exhibits much stronger and more stable cathodic and anodic peaks compared with ATMCNs ( Figures S3 and S4, Supporting Information), illustrating higher lithium storage density and easier lithium insertion/extraction reaction.…”

Investigating the Electrochemical Reversibility of Transition Metal Oxide Conversion Materials Through STEM-EELS

“…Unfortunately, conversion systems suffer from poor cycling issues due to irreversible phase transformations and the formation of electrically insulating reaction products (i.e. Li2O), among other technical challenges.[1]The conversion reaction mechanisms of several nanoscale transition metal oxides have been analyzed [2,3], but these studies largely focus on phase transformations during reaction and lack close analysis of the reaction products and their role in affecting reversibility. XANES studies have highlighted the importance of understanding interfacial structure and composition of reaction products in order to solve issues with irreversible cycling, due to their effects on electron and ion transport and electrochemical activity.…”