473 research outputs found
Real-time Measurement of Stress and Damage Evolution During Initial Lithiation of Crystalline Silicon
Crystalline to amorphous phase transformation during initial lithiation in
(100) silicon-wafers is studied in an electrochemical cell with lithium metal
as the counter and reference electrode. It is demonstrated that severe stress
jumps across the phase boundary lead to fracture and damage, which is an
essential consideration in designing silicon based anodes for lithium ion
batteries. During initial lithiation, a moving phase boundary advances into the
wafer starting from the surface facing the lithium electrode, transforming
crystalline silicon into amorphous LixSi. The resulting biaxial compressive
stress in the amorphous layer is measured in situ and it was observed to be ca.
0.5 GPa. HRTEM images reveal that the crystalline-amorphous phase boundary is
very sharp, with a thickness of ~ 1 nm. Upon delithiation, the stress rapidly
reverses, becomes tensile and the amorphous layer begins to deform plastically
at around 0.5 GPa. With continued delithiation, the yield stress increases in
magnitude, culminating in sudden fracture of the amorphous layer into
micro-fragments and the cracks extend into the underlying crystalline silicon.Comment: 12 pages, 5 figure
Effect of Diphenyl Siloxane on the Catalytic Activity of Pt on Carbon
The effect of silicone on the catalytic activity of Pt for oxygen reduction and hydrogen adsorption was studied using diphenyl siloxane as a source compound at a rotating disk electrode (RDE). Diphenyl siloxane did not affect the catalytic activity of Pt when it was injected into the electrolyte. However, it blocked the oxygen reduction reaction when it was premixed with the catalyst. Proton transport was not blocked in either case. We postulate that diphenyl siloxane induces hydrophobicity and causes local water starvation, thereby blocking oxygen transport. Hence, the slow leaching of silicone seals in a fuel cell could cause silicon accumulation in the electrode, which irreversibly degrades fuel cell performance by blocking oxygen transport to the catalyst sites
On the stranding of sei whale, Balaenoptera borealis Lesson at Mandapam along the Palk Bay coast
On 20th January, 1992, an adult female sei whale, measuring 14.0 m in total length and weighing about 10 tonnes stranded at Theedai near the marine fish farm of Central
Marine Fisheries Research Institute, Mandapam Camp
Lift-and-Round to Improve Weighted Completion Time on Unrelated Machines
We consider the problem of scheduling jobs on unrelated machines so as to
minimize the sum of weighted completion times. Our main result is a
-approximation algorithm for some fixed , improving upon the
long-standing bound of 3/2 (independently due to Skutella, Journal of the ACM,
2001, and Sethuraman & Squillante, SODA, 1999). To do this, we first introduce
a new lift-and-project based SDP relaxation for the problem. This is necessary
as the previous convex programming relaxations have an integrality gap of
. Second, we give a new general bipartite-rounding procedure that produces
an assignment with certain strong negative correlation properties.Comment: 21 pages, 4 figure
Fishing methods in coral reef areas of the Gulf of Mannar
Fishing methods being practised in the reef areas
of the Gulf of Mannar for finfishes are trawling,
gillnetting, fishing by hooks and lines and traps. Out of
these, the most important device is trawling by which
the most diverse and the highest quantity of finfishes
are being landed from coral reef areas in this region
Stress Evolution in Composite Silicon Electrodes during Lithiation/Delithiation
We report real-time average stress measurements on composite silicon
electrodes made with two different binders [Carboxymethyl cellulose (CMC), and
polyvinylidene fluoride (PVDF)] during electrochemical lithiation and
delithiation. During galvanostatic lithiation at very slow rates, the stress in
a CMC-based electrode becomes compressive and increases to 70 MPa, where it
reaches a plateau and increases slowly thereafter with capacity. The PVDF-based
electrode exhibits similar behavior, although with lower peak compressive
stress of about 12 MPa. These initial experiments indicate that the stress
evolution in a Si composite electrode depends strongly on the mechanical
properties of the binder. Stress data obtained from a series of
lithiation/delithiation cycles suggests plasticity induced irreversible shape
changes in contacting Si particles, and as a result, the stress response of the
system during any given lithiation/delithiation cycle depends on the cycling
history of the electrode. While these results constitute the first in-situ
stress measurements on composite Si electrodes during electrochemical cycling,
the diagnostic technique described herein can be used to assess the mechanical
response of a composite electrode made with other active material/binder
combinations.Comment: 22 pages, 8 figure
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