Inorganic Nanowires as Advanced Energy Conversion and Storage Materials

Yi CuiDepartment of Materials Science and Engineering

& Geballe Laboratory for Advance MaterialsStanford University

Science 293, 1289 (2001).

In the Past: NanowiresNanoelectronic devices

Science 291, 851 (2001).

Nanowire nanosensors

100 nm

Nano Lett. 5, 1519(2005) Nature 430, 190 (2004).

Quantum coupling devices

Inorganic Nanowires

Uniqueness of nanowires- Confinement effects- Large surface area- Transport carriers, photons, and ions- Facile strain relaxation- Well-defined nanoscale domain

NanowiresDiameter 1-200 nm, Length up to 100 μm

Nanowire-Based Research Program

Electrochem Bioprobe10 nm

R Oe

Phase-change memory

Crystalline Amorphous V+_

Ag

Metal bridge memory

Nonvolatile Memory

Nano Lett. 6, 1514 (2006). J. Am. Chem. Soc. 129, 34 (2007).

Solar Cells

CIGS

Nano Lett. 7, 199 (2007). J. Am. Chem. Soc. 129, 34 (2007). Nano Lett. 7, 1095 (2007).

MEG

Li Battery

Nano Lett. 7, 490 (2007). Nature Nanotech. (submitted).

TCE

With Peter Peumans

1. Nanowire Lithium Battery ElectrodesCandace K. Chan, Yuan YangCollaborator: Prof. Robert Huggins

Nano Lett. 7, 490 (2007).

Nature Nanotech. (submitted).

GCEP 3-yr project (Mar 2007 to Feb 2010): Yi Cui, Fritz Prinz

Battery parameters:- Energy density: cathode and anode- Power density: ion intercalation and electron transport- Cycle life: strain relaxation

Li Battery Technology

J.-M. Tarascon & M. Armand. Nature. 414, 359 (2001).

Nanowires as Li Battery Electrodes

What nano can offer: - New materials otherwise not possible: (high energy density).- Large surface area and shorter distance for Li diffusion (high power density).- Good strain release and interface control: (better cycle life).- Continuous electron transport pathway.

Example: Si as Anode Materials

C anodes: the existing anode technology.

C6 LiC6

Si anodes:

Theoretical capacity: 372 mA h/g

Si Li4.4Si

Theoretical capacity: 4200 mA h/g

Problem for Si: 400% volume expansion.

Vapor-Liquid-Solid (VLS) Growth of Si Nanowires

Au particles

Metal substrate

5 μm

10 nm10 nm

SiH4

Nanowire Battery Testing

Three electrode electrochemical measurements

Nanowire electrode(working)

Li foil(reference, counter)

Measured parameters: current, voltage, time.

• Si nanowires show 10 times higher capacity than the existing carbon anodes.• Si nanowires show much better cycle life than the bulk, particle and thin film.• The significance of Si anodes: abundant, mature infrastructure, no need of high purity.

Ultrahigh Capacity Si Nanowire Anodes

At C/20 rate

GCEP 1-yr exploratory project (Jan 2007 to Dec 2007): Yi Cui

2. Nanowires for Multiexciton Generation (MEG) Solar cells

Jia Zhu, Lifeng Cui

Zhu, Cui Nano Lett. 7, 199 ,2007

MEG Processes

(Klimov, Nozik etc.)

VB

CB

Nanocrystals

Increase coupling

Catalyst: In, Bi, Ga, Pb

In

Epitaxial Growth NaCl Substrate

Zhu, Cui Nano Lett. 7, 199 ,2007

3. CuInSe2 Nanowire Materials for Solar Cells

J. Am. Chem. Soc. 129, 34 (2007). Nano Lett. 7, 199 (2007).

Hailin Peng, David Schoen, Chong Xie

CIGS: 19.5% efficiency.

ZnO, ITO2500 Å

CdS700 Å

Mo0.5-1 µm

Glass,Metal Foil,

Plastics

CIGS1-2.5 µm

CIGS

CIGS Solar Cells

Issues- Grain boundary- Nanoscale phase inhomogeneity- CIGS-CdS Interface

(R. Noufi et. al.)

Cu-Rich CuInSe2 NWs

Chalcopyrite structure

26%:23%:51%

Cu:In:Se

Cu-Defficient CuInSe2 NWs

- Still Chalcopyrite structure, but with superlattices- Vacancy ordering

Cu:In:Se 15%:34%:51%

CuInSe2 NWs CdS Chemical Bath Deposition

CuInSe2-CdS Core-Shell NWs

5 min

e

Cu ions diffuse out

CuInSe2-CdS Core-Shell NWs

EDX mapping

CISOVC

CdS

OVC: ordered vacancy compound

CuInSe2-CdS Nanotubes

Increase CBD time up to 16min at 60C

12 min

16 min

Polycrystalline

Cu-In-Cd-Se-S Nanotubes

Nanoscale Kirkendal effect:Alivisatos Science 304, 711 (2004).