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Abstract Layered transition‐metal dichalcogenides (TMDs) have shown promise to replace carbon‐based compounds as suitable anode materials for Lithium‐ion batteries (LIBs) owing to facile intercalation and de‐intercalation of lithium (Li) during charging and discharging, respectively. While the intercalation mechanism of Li in mono‐ and bi‐layer TMDs has’ been thoroughly examined, mechanistic understanding of Li intercalation‐induced phase transformation in bulk or films of TMDs is still largely unexplored. This study investigates possible scenarios during sequential Li intercalation and aims to gain a mechanistic understanding of the phase transformation in bulk MoS2using density functional theory (DFT) calculations. The manuscript examines the role of concentration and distribution of Li‐ions on the formation of dual‐phase 2H‐1T microstructures that have been observed experimentally. The study demonstrates that lithiation would proceed in a systematic layer‐by‐layer manner wherein Li‐ions diffuse into successive interlayer spacings to render local phase transformation of the adjacent MoS2layers from 2H‐to‐1T phase in the multilayered MoS2. This local phase transition is attributed to partial ionization of Li and charge redistribution around the metal atoms and is followed by subsequent lattice straining. In addition, the stability of single‐phase vs. multiphase intercalated microstructures, and the origins of structural changes accompanying Li‐ion insertion are investigated at atomic scales.
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Atomic‐Scale Visualization of Electrochemical Lithiation Processes in Monolayer MoS 2 by Cryogenic Electron Microscopy
Abstract While lithium ion batteries with electrodes based on intercalation compounds have dominated the portable energy storage market for decades, the energy density of these materials is fundamentally limited. Today, rapidly growing demand for this type of energy storage is driving research into materials that utilize alternative reaction mechanisms to enable higher energy densities. Transition metal compounds are one such class of materials, with storage enabled by “conversion” reactions, where the material is converted to new compound upon lithiation. MoS2is one example of this type of material that has generated a large amount of interest recently due to its high theoretical lithium storage capacity compared to graphite. Here, cryogenic scanning transmission electron microscopy techniques are used to reveal the atomic‐scale processes that occur during reaction of a model monolayer MoS2system by enabling the unaltered atomic structure to be determined at various levels of lithiation. It is revealed that monolayer MoS2can undergo a conversion reaction even with no substrate, and that the resulting particles are smaller than those that form in bulk MoS2, likely due to the more limited 2D diffusion. Additionally, while bilayer MoS2undergoes intercalation with a corresponding phase transition before conversion, monolayer MoS2does not.
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- PAR ID:
- 10459590
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 9
- Issue:
- 47
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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