3 research outputs found
Fragmented Carbon Nanotube Macrofilms as Adhesive Conductors for Lithium-Ion Batteries
Polymer binders such as poly(vinylidene fluoride) (PVDF) and conductive additives such as carbon black (CB) are indispensable components for manufacturing battery electrodes in addition to active materials. The concept of adhesive conductors employing fragmented carbon nanotube macrofilms (FCNTs) is demonstrated by constructing composite electrodes with a typical active material, LiMn<sub>2</sub>O<sub>4</sub>. The adhesive FCNT conductors provide not only a high electrical conductivity but also a strong adhesive force, functioning simultaneously as both the conductive additives and the binder materials for lithium-ion batteries. Such composite electrodes exhibit superior high-rate and retention capabilities compared to the electrodes using a conventional binder (PVDF) and a conductive additive (CB). An <i>in situ</i> tribology method combining wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The adhesive FCNT conductors exhibit higher adhesion strength than PVDF. It has further been confirmed that the adhesive FCNT conductor can be used in both cathodes and anodes and is proved to be a competent substitute for polymer binders to maintain mechanical integrity and at the same time to provide electrical connectivity of active materials in the composite electrodes. The organic-solvent-free electrode manufacturing offers a promising strategy for the battery industry
Anomalous Capacitive Behaviors of Graphene Oxide Based Solid-State Supercapacitors
Substantial
differences in charge storage mechanisms exist between
dielectric capacitors (DCs) and electrochemical capacitors (ECs),
resulting in orders of magnitude difference of stored charge density
in them. However, if ionic diffusion, the major charge transport mechanism
in ECs, is confined within nanoscale dimensions, the Helmholtz layers
and diffusion layers will overlap, resulting in dismissible ionic
diffusion. An interesting contradiction between appreciable energy
density and unrecognizable ionic diffusion is observed in solid-state
capacitors made from reduced graphene oxide films that challenge the
fundamental charge storage mechanisms proposed in such devices. A
new capacitive model is proposed, which combines the two distinct
charge storage mechanisms of DCs and ECs, to explain the contradiction,
of high storage capacity yet undetectable ionic diffusion, seen in
graphene oxide based supercapacitors
Three-Dimensional Nitrogen-Doped Multiwall Carbon Nanotube Sponges with Tunable Properties
A three-dimensional (3D) nitrogen-doped
multiwall carbon nanotube (N-MWCNT) sponge possessing junctions induced
by both nitrogen and sulfur was synthesized by chemical vapor deposition
(CVD). The formation of “elbow” junctions as well as
“welded” junctions, which are attributed to the synergistic
effect of the nitrogen dopant and the sulfur promoter, plays a critically
important role in the formation of 3D nanotube sponges. To the best
of our knowledge, this is the first report showing the synthesis of
macroscale 3D N-MWCNT sponges. Most importantly, the diameter of N-MWCNT
can be simply controlled by varying the concentration of sulfur, which
in turn controls both the sponge’s mechanical and its electrical
properties. It was experimentally shown that, with increasing diameter
of N-MWCNT, the elastic modulus of the sponge increased while the
electrical conductivity decreased. The mechanical behaviors of the
sponges have also been quantitatively analyzed by employing strain
energy function modeling