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.
Nanoscale morphology has a direct impact on the performance of materials for electrochemical energy storage. Despite this importance, little is known about the evolution of primary particle morphology nor its effect on chemical pathways during synthesis. In this study, operando characterization is combined with atomic‐scale and continuum simulations to clarify the relationship between morphology of cathode primary particles and their lithiation during calcination of LiNi0.8Mn0.1Co0.1O2(NMC‐811). This combined approach reveals a key role for surface oxygen adsorption in facilitating the lithiation reaction by promoting metal diffusion and oxidation, and simultaneously providing surface sites for lithium insertion. Furthermore, oxygen surface termination is shown to increase the activation energy for sintering, leading to smaller primary particle sizes at intermediate temperatures. Smaller particles provide both shorter diffusion lengths for lithium incorporation and increased surface site density for lithium insertion. These insights provide a foundation for more tailored syntheses of cathode materials with optimized performance characteristics.
more » « less- NSF-PAR ID:
- 10366615
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 12
- Issue:
- 16
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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