Ph.D defense Candace K. Chan, Monday June 8 @ 2pm, Braun Lec
candacec at stanford.edu
Sat May 30 15:55:46 PDT 2009
*One-dimensional nanostructured materials for Li-ion battery and
Candace K. Chan (Dept. of Chemistry)
Adviser: Yi Cui (Dept. of Materials Science & Engineering)
Monday, June 8 @ 2 pm (Refreshments served at 1:45 pm)
Braun Lecture Hall (Mudd Chemistry Building)
The need for improved electrochemical storage devices has necessitated
research on new and advanced electrode materials. One-dimensional
nanomaterials such as nanowires, nanotubes, and nanoribbons, can provide
a unique opportunity to engineer electrochemical devices to have
improved electronic and ionic conductivity as well as electrochemical
and structural transformations. Several properties of nanomaterials,
including 1) facile strain relaxation and phase transformation, 2) good
ionic diffusion, and 3) good electronic conduction are important
characteristics that allow for improvements in performance over bulk
materials. Several examples of how nanomaterials are being used to
improve problems in energy storage will be given, with discussion on
fundamental and applied studies at the single nanowire and ensemble
level all the way up to the nanocomposite level.
A study on the phase transformations in V2O5 nanoribbons during reaction
with lithium will be presented, with implications for Li-ion cathodes.
Transformation of the V2O5 nanoribbons into the fully lithiated
?-Li3V2O5 phase was found to depend not only on the width but also the
thickness of the nanoribbons. For the first time, complete delithiation
of ?-Li3V2O5 back to the single-crystalline, pristine V2O5 nanoribbon
was observed, indicating a 30% higher energy density.
For Li-ion battery anodes, the use of Si and Ge nanowires (NWs) as high
capacity replacements for graphite will be discussed. By using a SiNW
electrode, a 10X higher specific capacity was achieved. Problems
plaguing bulk Si, such as pulverization and poor charge storage
retention, were not observed in the SiNWs due to the NWs having improved
accommodation of strain and volume expansion.
Finally, an entirely printable supercapacitor device will be presented
based on high surface area carbons and a flexible, printable silver
nanowire-based current collector. These devices demonstrate how
nanomaterials can be integrated into a roll-to-roll manufacturing
process while still displaying good performance.
Candace K. Chan
Ph.D. Student, Department of Chemistry
McCullough Building Room 209
476 Lomita Mall
Stanford, CA 94305
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