Nanowire Lithium-Ion Batteries as Advanced Electrochemical Energy Storage

Yi CuiDepartment of Materials Science and Engineering

& Geballe Laboratory for Advance MaterialsStanford University

Importance of Energy Storage

Portable Electronics

Implantable Devices

Vehicle Electrification

Tesla Roadster

Storage for Renewable Energy and Grid

Solar Wind

Energy Storage Technologies

+++++

-----

Capacitor

+++++

-----

Supercapacitor (Electrochemical capacitor)

solution

Metal

dielectricsElectrical double layer

Metal

2

21 CVE =

Batteries (Ag-Zn)

FVGZnAgZnAgZneZnAgeAg

2,22

2

2

−=Δ+⎯→⎯+

⎯→⎯−

⎯→⎯+

++

+−

−+

Reaction free energy Faraday constant

Battery voltage

http://en.wikipedia.org/wiki/Fuel_cell

Fuel Cells

Specific energy (wh/kg)

Spec

ific

pow

er (w

/kg)

10-2 10-1 1 10 102 1031

10

102

103

104

105

106 Capacitors

Supercapacitors

Batteries Fuel cells

Comparison of Energy Storage Technologies

Important parameters:- Energy density (Energy per weight or volume)- Power density (Power per weight or volume)- Cycle life and safety- Cost

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

Why Li Ion Batteries?

Li-related batteries have larger energy density than other batteries.

Existing Li Ion Battery Technology

1. Energy density: - Anode and cathode Li storage capacity- Voltage

2. Power density: - Li ion moving rate- Electron transport

3. Cycle, calendar life and safety: strain relaxation and chemical stability.4. Cost: Abundant and cheap materials

Graphite: 370 mAh/gLiCoO2: 140 mAh/g

The energy density can not meetthe application needs.

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

Electrode Materials

Anode: low potentialCathode: high potential

Two Types of Electrode Materials

Existing Tech. Future Tech.New Materials

Mechanism Intercalation Displacement/alloy

Volume change Small Large

Li diffusion rate Fast Slow

Specific capacity Low High

Li Li

We work on the future generation of battery materials.

C. K. Chan, Y. Cui and co-workers, Nano Letters 7, 490 (2007).C. K. Chan, Y. Cui and co-workers, Nano Letters 8, 307 (2007)C. K. Chan, R. Huggins, Y. Cui and co-workers Nature Nanotechnology 3, 31 (2008)

Nanowires as Li Battery Electrodes

What nanowires can offer: - Good strain relaxation: new materials possible- Large surface area and shorter distance for Li diffusion- Interface control: (better cycle life).- Continuous electron transport pathway.

Example: Si as Anode Materials

C anode: the existing anode technology.

C6 LiC6

Si anode

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 nanoparticles

Metal substrate

5 μm

SiH4 400-500 ºCchemical vapor deposition

Au Nanoparticles:Scanning Electron Micrograph

Si NanowiresScanning Electron Micrograph

10 nm10 nm

Structure of Si Nanowires

High Resolution Transmission Electromicrograph

- Single crystal- 1-3 nm amorphous SiO2

Nanowire Battery Testing

Measured parameters: current, voltage, time.

Beaker Cell Flat Cell

• 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.

Ultrahigh Capacity Si Nanowire AnodesAt C/20 rate

C. K. Chan, R. Huggins, Y. Cui and co-workers Nature Nanotechnology 3, 31 (2008)

Power Rate-Dependence

Diameter Change of Si Nanowire Anodes

Before

After

The diameter changes to 150% but nanowires don’t break.

Length Change of Si Nanowire Anodes

After Li-cyclingBefore Li-cyclingEDX mapping

Structure Change of Si Nanowire Anodes

X-ray diffraction

Li insertion

Structure Change of Si Nanowire Anodes

Li insertion progressionHRTEM100 mV 50 mV 10 mVPristine

Acknowledgement

Candace K. ChanProf Robert Huggins