Engineering multifunctional superstructure cathodes to
conquer
the critical issue of sluggish kinetics and large volume changes associated
with divalent Zn-ion intercalation reactions is highly desirable for
boosting practical Zn-ion battery applications. Herein, it is demonstrated
that a MoS2/C19H42N+ (CTAB)
superstructure can be rationally designed as a stable and high-rate
cathode. Incorporation of soft organic CTAB into a rigid MoS2 host forming the superlattice structure not only effectively initiates
and smooths Zn2+ transport paths by significantly expanding
the MoS2 interlayer spacing (1.0 nm) but also endows structural
stability to accommodate Zn2+ storage with expansion along
the MoS2 in-plane, while synchronous shrinkage along the
superlattice interlayer achieves volume self-regulation of the whole
cathode, as evidenced by in situ synchrotron X-ray
diffraction and substantial ex situ characterizations.
Consequently, the optimized superlattice cathode delivers high-rate
performance, long-term cycling stability (∼92.8% capacity retention
at 10 A g–1 after 2100 cycles), and favorable flexibility
in a pouch cell. Moreover, a decent areal capacity (0.87 mAh cm–2) is achieved even after a 10-fold increase of loading
mass (∼11.5 mg cm–2), which is of great significance
for practical applications. This work highlights the design of multifunctional
superlattice electrodes for high-performance aqueous batteries.
The migration of gold atoms attached to single vacancies near the edges of graphene ribbons is studied using density-functional theory calculations. The stable position for a single gold atom is found to be on top of a vacancy, as in an infinite graphene sheet. An energy of 5 eV is needed for the Au atom to move through the vacancy to the other side of the sheet, but the Au atom can migrate in lateral direction together with the vacancy, with a migration barrier of about 2.2 eV. The sites near the edges of the graphene layer are energetically more favorable for gold-atom-vacancy pairs than sites in the middle of extended graphene layers. The migration barriers for different pathways show that it is easier for the gold atom to move toward the edge where it can be captured. When the gold atom reaches the edge, it can migrate along the edge with an energy barrier of only 1.4 eV. Our results explain recent experimental observations ͓Y. Gan et al., Small 4, 587 ͑2008͔͒ and provide information on the dynamics of metal atoms on substitutional sites in graphene as well as on their agglomeration at defects and at edges of graphene ribbons.
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