4 research outputs found
Numerical Modeling of Fracture-Resistant Sn Micropillars as Anode for Lithium Ion Batteries
Sn possesses three times higher capacity
in comparison to graphite
anode (372 mAhg<sup>–1</sup>) that makes it a promising candidate
for enhanced performance Li ion batteries. Contrary to Si, Sn is compliant
and ductile in nature and thus is expected to readily relax the Li
diffusion-induced stresses. The low melting point of Sn additionally
allows for stress relaxations from time-dependent or creep deformations
even at room temperature. In this study, numerical modeling is used
to reveal the significance of plasticity and creep-based stress relaxations
in the Sn working electrode. The maximum elastic tensile hoop stresses
for 1 μm micropillar size with 1<i>C</i> charging
rate conditions reduces down from ∼1 GPa to ∼200 MPa
when Sn is allowed to plastically deform at a yield strength of ∼150
MPa. After experimentally determining the creep response of Sn micropillars,
creep deformations are incorporated in numerical modeling to show
that the maximum tensile hoop stress is further reduced to ∼0.45
MPa under the same conditions. Lastly, the Li-induced stresses are
analyzed for different micropillar sizes to evaluate the critical
size to prevent fracture, which is determined to be ∼5.3 μm
for <i>C</i>/10 charging rate, which is significantly larger
than that in Si
Polypyrrole–MnO<sub>2</sub>‑Coated Textile-Based Flexible-Stretchable Supercapacitor with High Electrochemical and Mechanical Reliability
Carbon-nanotube
(CNT)-based textile supercapacitors with MnO<sub>2</sub> nanoparticles
have excellent power and energy densities,
but MnO<sub>2</sub> nanoparticles can be delaminated during charge–discharge
cycles, which results in significant degradation in capacitance. In
this study, polypyrrole conductive polymer was coated on top of MnO<sub>2</sub> nanoparticles that are deposited on CNT textile supercapacitor
to prevent delamination of MnO<sub>2</sub> nanoparticles. An increase
of 38% in electrochemical energy capacity to 461 F/g was observed, while
cyclic reliability also improved, as 93.8% of energy capacity was
retained over 10 000 cycles. Energy density and power density
were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in
situ electrochemical–mechanical study revealed that polypyrrole–MnO<sub>2</sub>-coated CNT textile supercapacitor can retain 98.5% of its
initial energy capacity upon application of 21% tensile strain and
showed no observable energy storage capacity change upon application
of 13% bending strain. After imposing cyclic bending of 750 000
cycles, the capacitance was retained to 96.3%. Therefore, the results
from this study confirmed for the first time that the polypyrrole–MnO<sub>2</sub>-coated CNT textile can reliably operate with high energy
and power densities with in situ application of both tensile and bending
strains
Highly Transparent Au-Coated Ag Nanowire Transparent Electrode with Reduction in Haze
Ag nanowire transparent electrode
has excellent transmittance and sheet resistance, yet its optical
haze still needs to be improved in order for it to be suitable for
display applications. Ag nanowires are known to have high haze because
of the geometry of the nanowire and the high light scattering characteristic
of the Ag. In this study, a Au-coated Ag nanowire structure was proposed
to reduce the haze, where a thin layer of Au was coated on the surface
of the Ag nanowires using a mild [AuÂ(en)<sub>2</sub>]ÂCl<sub>3</sub> galvanic displacement reaction. The mild galvanic exchange allowed
for a thin layer of Au coating on the Ag nanowires with minimal truncation
of the nanowire, where the average length and the diameter were 13.0
μm and 60 nm, respectively. The Au-coated Ag nanowires were
suspended in methanol and then electrostatically sprayed on a flexible
polycarbonate substrate that revealed a clear reduction in haze with
a 2–4% increase in total transmittance, sheet resistance ranges
of 80–90%, and 8.8–36.8 Ohm/sq. Finite difference time
domain simulations were conducted for Au-coated Ag nanowires that
indicated a significant reduction in the average scattering from 1
to 0.69 for Au layer thicknesses of 0–10 nm
Role of Graphene in Reducing Fatigue Damage in Cu/Gr Nanolayered Composite
Nanoscale
metal/graphene nanolayered composite is known to have ultrahigh
strength as the graphene effectively blocks dislocations from penetrating
through the metal/graphene interface. The same graphene interface,
which has a strong sp2 bonding, can simultaneously serve as an effective
interface for deflecting the fatigue cracks that are generated under
cyclic bendings. In this study, Cu/Gr composite with repeat layer
spacing of 100 nm was tested for bending fatigue at 1.6% and 3.1%
strain up to 1,000,000 cycles that showed for the first time a 5–6
times enhancement in fatigue resistance compared to the conventional
Cu thin film. Fatigue cracks that are generated within the Cu layer
were stopped by the graphene interface, which are evidenced by cross-sectional
scanning electron microscopy and transmission electron microscopy
images. Molecular dynamics simulations for uniaxial tension of Cu/Gr
showed limited accumulation of dislocations at the film/substrate
interface, which makes the fatigue crack formation and propagation
through thickness of the film difficult in this materials system