3 research outputs found
Anomalous Li Storage Capability in Atomically Thin Two-Dimensional Sheets of Nonlayered MoO<sub>2</sub>
Since
the first exfoliation and identification of graphene in 2004,
research on layered ultrathin two-dimensional (2D) nanomaterials has
achieved remarkable progress. Realizing the special importance of
2D geometry, we demonstrate that the controlled synthesis of nonlayered
nanomaterials in 2D geometry can yield some unique properties that
otherwise cannot be achieved in these nonlayered systems. Herein,
we report a systematic study involving theoretical and experimental
approaches to evaluate the Li-ion storage capability in 2D atomic
sheets of nonlayered molybdenum dioxide (MoO<sub>2</sub>). We develop
a novel monomer-assisted reduction process to produce high quality
2D sheets of nonlayered MoO<sub>2</sub>. When used as lithium-ion
battery (LIB) anodes, these ultrathin 2D-MoO<sub>2</sub> electrodes
demonstrate extraordinary reversible capacity, as high as 1516 mAh
g<sup>–1</sup> after 100 cycles at the current rate of 100
mA g<sup>–1</sup> and 489 mAh g<sup>–1</sup> after 1050
cycles at 1000 mA g<sup>–1</sup>. It is evident that these
ultrathin 2D sheets did not follow the normal intercalation-cum-conversion
mechanism when used as LIB anodes, which was observed for their bulk
analogue. Our ex situ XPS and XRD studies reveal a Li-storage mechanism
in these 2D-MoO<sub>2</sub> sheets consisting of an intercalation
reaction and the formation of metallic Li phase. In addition, the
2D-MoO<sub>2</sub> based microsupercapacitors exhibit high areal capacitance
(63.1 mF cm<sup>–2</sup> at 0.1 mA cm<sup>–2</sup>),
good rate performance (81% retention from 0.1 to 2 mA cm<sup>–2</sup>), and superior cycle stability (86% retention after 10,000 cycles).
We believe that our work identifies a new pathway to make 2D nanostructures
from nonlayered compounds, which results in an extremely enhanced
energy storage capability