Nanowire Lithium-Ion Batteries as. Advanced Electrochemical Energy Storage. Yi
Cui. Department of Materials Science and Engineering. & Geballe Laboratory ...
Nanowire Lithium-Ion Batteries as Advanced Electrochemical Energy Storage Yi Cui Department of Materials Science and Engineering & Geballe Laboratory for Advance Materials Stanford University
Importance of Energy Storage Portable Electronics
Vehicle Electrification Tesla Roadster
Implantable Devices
Storage for Renewable Energy and Grid Solar
Wind
Energy Storage Technologies
Capacitor + + + + Metal +
-
Supercapacitor (Electrochemical capacitor)
Metal
+ + + + +
- solution -
Electrical double layer dielectrics
1 E = CV 2 2
Batteries (Ag-Zn)
Ag + + e − ⎯ ⎯→ Ag −
Zn − 2e ⎯ ⎯→ Zn
2+
Battery voltage
2 Ag + + Zn ⎯ ⎯→ Ag + Zn 2+ , ΔG = −2 FV Reaction free energy
Faraday constant
Fuel Cells
http://en.wikipedia.org/wiki/Fuel_cell
Specific power (w/kg)
Comparison of Energy Storage Technologies 106
Capacitors
105 104
Supercapacitors
103 102
Batteries Fuel cells
10 1 10-2
10-1
1
10
102
103
Specific energy (wh/kg)
Important parameters: - Energy density (Energy per weight or volume) - Power density (Power per weight or volume) - Cycle life and safety - Cost
Why Li Ion Batteries?
Li-related batteries have larger energy density than other batteries. J.-M. Tarascon & M. Armand. Nature 414, 359 (2001).
Existing Li Ion Battery Technology Graphite: 370 mAh/g LiCoO2: 140 mAh/g The energy density can not meet the application needs.
1. 2. 3. 4.
Energy density: - Anode and cathode Li storage capacity - Voltage Power density: - Li ion moving rate - Electron transport Cycle, calendar life and safety: strain relaxation and chemical stability. Cost: Abundant and cheap materials
Electrode Materials
Anode: low potential Cathode: high potential J.-M. Tarascon & M. Armand. Nature. 414, 359 (2001).
Two Types of Electrode Materials Li
Li
Existing Tech.
Future Tech. New Materials
Mechanism
Intercalation
Displacement/alloy
Volume change
Small
Large
Li diffusion rate
Fast
Slow
Specific capacity
Low
High
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
Theoretical capacity: 372 mA h/g
Si anode 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
SiH4 400-500 ºC chemical vapor deposition
Metal substrate
Au Nanoparticles: Scanning Electron Micrograph
Si Nanowires Scanning Electron Micrograph
5 μm
Structure of Si Nanowires High Resolution Transmission Electromicrograph
10 nm
10 nm
- Single crystal - 1-3 nm amorphous SiO2
Nanowire Battery Testing Beaker Cell
Flat Cell
Measured parameters: current, voltage, time.
Ultrahigh Capacity Si Nanowire Anodes At C/20 rate
• 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.
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 EDX mapping Before Li-cycling
After Li-cycling
Structure Change of Si Nanowire Anodes X-ray diffraction
Li insertion
Structure Change of Si Nanowire Anodes HRTEM Pristine
