Rational design of materials for
energy storage systems relies
on our ability to probe these materials at various length scales.
Solid-state NMR spectroscopy is a powerful approach for gaining chemical
and structural insights at the atomic/molecular level, but its low
detection sensitivity often limits applicability. This limitation
can be overcome by transferring the high polarization of electron
spins to the sample of interest in a process called dynamic nuclear
polarization (DNP). Here, we employ for the first time metal ion-based
DNP to probe pristine and cycled composite battery electrodes. A new
and efficient DNP agent, Fe(III), is introduced, yielding lithium
signal enhancement up to 180 when substituted in the anode material
Li4Ti5O12. In addition for being
DNP active, Fe(III) improves the anode performance. Reduction of Fe(III)
to Fe(II) upon cycling can be monitored in the loss of DNP activity.
We show that the dopant can be reactivated (return to Fe(III)) for
DNP by increasing the cycling potential window. Furthermore, we demonstrate
that the deleterious effect of carbon additives on the DNP process
can be eliminated by using carbon free electrodes, doped with Fe(III)
and Mn(II), which provide good electrochemical performance as well
as sensitivity in DNP-NMR. We expect that the approach presented here
will expand the applicability of DNP for studying materials for frontier
challenges in materials chemistry associated with energy and sustainability.
We unveil that the conformational
change of a single organic molecule
during the redox reaction leads to impressive battery performance
for the first time. We propose the model material, a phenoxazin-3-one
derivative, as a new redox-active bioinspired single molecule for
the Li-ion rechargeable battery. The phenoxazin-3-one cathode delivered
a high discharge capacity (298 mAh g–1) and fast
rate capability (65% capacity retention at 10 C). We elaborate the
redox mechanism and reaction pathway of phenoxazin-3-one during Li+-coupled redox reaction. The molecular structure alteration
of phenoxazin-3-one during the lithium-coupled electron transfer reaction
enables strong π–π interaction between 2Li-phenoxazin-3-one
and carbon, which was evidenced by operando Raman
spectroscopy and density functional theory calculation. Our work provides
in-depth understanding about the conformational molecular switch of
the single molecule during Li+-coupled redox reaction and
insight into the design of a new class of organic electrode materials.
The lithium–sulfur cell is
considered to be the most promising
next-generation energy storage system. However, the practical use
of Li–S batteries is hindered by several problems such as poor
cycle retention, low Coulombic efficiency, low sulfur loading, and
so forth. We herein for the first-time propose nitrogen-doped graphene
quantum dots as the sulfiphilic additive for the advancement of Li–S
cell performance. We carry out direct decoration of conducting additives
and carbon cloth interlayers with graphene quantum dots and nitrogen-doped
graphene quantum dots, which are evaluated in Li–S cells. Nitrogen-doped
graphene quantum dots exhibit strong sulfiphilic properties, and therefore,
they anchor the liquid-phase polysulfides. The Li–S cell using
the nitrogen-doped graphene quantum dot-decorated carbon cloth interlayer
shows a discharge capacity of 1454.4 mA h gS
–1 at 0.1 C and a capacity retention of 98.2% at 0.5 C after 300 cycles
even with a sulfur loading of 6.0 mg S cm–2. Our
study demonstrates that the nitrogen-doped graphene quantum dot is
a promising additive, which can improve the viability of Li–S
cells for the next generation of energy storage systems.
We study the structural and electrochemical performance of sulfur cathodes prepared with two different binders, PVdF and SBR/CMC. Enhanced battery performance is observed in the SBR/CMC-based electrode and its origin is scrutinized.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.