Ph.D defense Candace K. Chan, Monday June 8 @ 2pm, Braun Lec

Candace Chan candacec at
Sat May 30 15:55:46 PDT 2009

*One-dimensional nanostructured materials for Li-ion battery and 
supercapacitor electrodes*

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
Stanford University
McCullough Building Room 209
476 Lomita Mall
Stanford, CA 94305

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