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

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)

Abstract 

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 ω-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 ω-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