The Effect of Mechanical Strain on Lithium Staging in Graphene

Abstract

The development of next‐generation electrodes for metal‐ion batteries requires an understanding of intercalation dynamics in nanomaterials. Herein, it is shown that microscale mechanical strain significantly affects the formation of ordered lithium phases in graphene. In situ Raman spectroscopy of graphene microflakes mechanically constrained at the edge during lithium intercalation reveals a thickness‐dependent increase of up to 1.26 V in the electrochemical potential that induces lithium staging. While the induced mechanical strain energy increases with graphene thickness to the fourth power, its magnitude is small compared to the observed increase in electrochemical energy. It is hypothesized that the mechanical strain energy increases a nucleation barrier for lithium staging, greatly delaying the formation of ordered lithium phases. These results indicate that electrode assembly may critically impact lithium staging dynamics. The present work demonstrates strain engineering in two dimensional (2D) nanomaterials as an effective approach to manipulate phase transitions and chemical reactivity.

Heterointerface Control over Lithium-Induced Phase Transitions in MoS2 Nanosheets: Implications for Nanoscaled Energy Materials

“…MoS 2 flake thickness was identified via the separation between the E 2g and A 1g Raman modes , measured using Raman spectroscopy (Figure S1). Graphene flake thickness was determined via the ratio of the intensity of the Si Raman peak at 520 cm ‑1 measured through the flake as compared to the intensity of the Si peak measured directly from the substrate, as we previously described . Raman analysis shows a low defect density in the graphene flakes (Figure S1).…”

“…Graphene flake thickness was determined via the ratio of the intensity of the Si Raman peak at 520 cm -1 measured through the flake as compared to the intensity of the Si peak measured directly from the substrate, as we previously described. 48 Raman analysis shows a low defect density in the graphene flakes (Figure S1). hBN flake thickness was estimated using optical microscopy.…”

“…Flakes of desired size and thickness were transferred to SiO 2 /Si substrates using a KOH-assisted technique, as we described previously. , Heterostructures were fabricated by repeating the flake transfer and using the micro-manipulator and a rotational stage to carefully control the placement of the second flake on top of the previously transferred bottom flake. All MoS 2 flakes used in this study were 5–7 layers thick, all graphene support flakes were 6–10 layers thick, and all graphene flakes covering MoS 2 were 5 layers thick to minimize the attenuation of the Raman signal from MoS 2 .…”

Revisiting Intercalation‐Induced Phase Transitions in 2D Group VI Transition Metal Dichalcogenides

“…[ 24 ] The effects of strain were experimentally observed to delay the lithium staging in several‐layer‐thick graphene flakes. [ 37 ]…”

“…For example, by collecting in situ Raman of graphene flakes during Li intercalation, Cha and coworkers quantitatively established the correlation between the nucleation barrier of Li staging transition in graphene and the amount of mechanical strain exerted on graphene by the electrode clamping. [ 37 ] Smet and coworkers revealed a super dense three‐layer Li ordering in between two graphene layers with the aid of in situ TEM. [ 39 ] Systematic in situ studies of other 2D materials will greatly deepen our microscopic understanding of intercalation and phase transitions.…”