Center for Composite Materials - University of Delaware

Research Summary

Understanding the Role of Carbon Nanotubes at the Substrate Silicon Electrode Interface

Authors: Mike Meck, Dr. Hertz, Dr. Wei

Motivation

The goal is to find a more efficient electrochemical energy storage device by improving the capacity and life span of batteries

The current in batteries is driven by the transfer of lithium ions between the anode and cathode due to oxidation and reduction reactions

Silicon is an optimal material for anode films in batteries
-- Low discharge potential
-- High charge capacity

Problem & Goal

- Silicon expands to accept lithium ions
- The volumetric expansions causes internal pressure
- Silicon breaks down to release pressure
-- Capacity fading

- A layer of single-walled carbon nanotubes (SWNT) is placed at substrate-silicon electrode interface
- The SWNT holds the silicon together
-- Tolerant of volumetric expansion
-- Internal pressure is relieved by releasing cone-shaped grains

Process

Sputtering

- Sputtering is a method of effectively depositing thin films of a variety of materials

- A high vacuum chamber ensures a large mean free path of particles

- Controllable variables power, deposition time, substrate temperature, bias voltage, and pressure.

Progress

- Eight sample sets have been made by manipulating the following variables for both types of substrate

- Four samples have been made into coin cell batteries at 75W, 4hrs, at both temperatures variables; with and without nanotubes

Testing

Scanning Electron Microscopy (SEM)

Electrochemical Impedance Spectroscopy
Series Resistance
Diffusion Resistance
Charge Transfer Resistance

Cyclability Testing
- Life cycle testing is done using repeated charge discharge cycles to measure the charge retention of the battery

Future Work

Which methods of processing silicon produce the anode with ideal properties?
- Power
- Thickness
- Heat

Acknowledgements and Bibliography

Thanks to:
Dr. Hertz Dr. Wei
UD Undergraduate Research Program
UD Center for Composite Materials
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Voelcker, John. "Lithium Batteries Take to the Road." IEEE Spectrum. N.p., Sept. 2007. Web. 01 Aug. 2012. <http://spectrum.ieee.org/green-tech/advanced-cars/lithium-batteries-take-to-the-road/2>. HowStuffWorks

Yang Shao-Horn, Laurence Croguennec, Claude Delmas, E. Chris Nelson and Michael A. O'Keefem (July 2003). "Atomic resolution of lithium ions in LiCoO2". Nature Materials 2 (7): 464 - 467. DOI:10.1038/nmat922

Rong, Jiepong. Single-Walled Carbon Nanotube Film for Electrochemical Energy Storage Devices. Thesis. University of Delaware, Spring 2010. N.p.: n.p., n.d. Print.

Gaia Technologies. "Gaia 3D Solutions for Schools, Colleges & Universities." Carbon Nanotube -. N.p., n.d. Web. 03 Aug. 2012. <http://www.gaia3d.co.uk/3d-models/3d-chemistry/carbon-nanotube/>.

Harrison, Karl. "Ferrocene." 3DChem. N.p., n.d. Web. 2 Aug. 2012. <http://www.3dchem.com/molecules.asp?ID=33>.

Rapid Electronics Limited. "GP Lithium Coin Cell Batteries." GP Lithium Coin Cell Batteries. N.p., n.d. Web. 02 Aug. 2012. <http://www.rapidonline.com/Electrical-Power/GP-Lithium-Coin-Cell-Batteries-74895>.

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