Silicon Nanowires for Rechargeable Li-Ion BatteriesOnur Ergen, Brian Lambson, Anthony YehEE C235, Spring 2009
Overview Battery Technology Landscape
Battery Basics Lithium Ion Battery State of the Art
Silicon Nanowire Anode Why Silicon Nanowires? Experimental Results Technical Comparison
Economic Perspective Market Analysis Future Outlook Conclusion
Battery BasicsLithium Ion BatteryState of the Art
Battery Technology Landscape
Nanowire Batteries
Motivation: Batteries and Life
How does a battery work?
History of Batteries
Lithium-ion Batteries
J.-M. Tarascon& M. Armand. Nature. 414, 359 (2001).
How do Li-ion batteries work? Battery Parameters
Energy density: cathode and anode
E (Wh) = voltage x capacity Power density: ion intercalation
and electron transport Cycle life: strain relaxation
Advantages of Li-ion batteries High cell voltage Superior energy and power
density High cycling stability Low self-discharge No memory or lazy battery effect 100% depth of discharge possible
What we have in daily technology
How can we improve from here?
Using silicon nanowires as anode Energy capacity Peak power Endurance Manufacture cost
Why Silicon Nanowires?Experimental ResultsTechnical Comparison
Silicon Nanowire Anode
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Silicon: an optimal anode material Graphite energy density: 372 mA h/g
Silicon energy density: 4200 mA h/g
C6LiC6
Si Li4.4Si
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Why haven’t we been using Si anodes?
Lithiation of silicon has one major problem – it is accompanied by a 400% volume
increase!
Chan et. al, Nature Nanotech, 2007
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Solution: Silicon Nanowires 10 x energy density of current anodes Structurally stable after many cycles
Chan et. al, Nature Nanotech, 2007
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Experimental Technique NW growth on stainless steel by vapor-liquid-solid (VLS)
technique Crystalline Si Core-shell (core = crystalline Si, shell = amorphous Si)
Test current-voltage characteristics over many charge/discharge cycles using cyclic voltammetry
C
Si NW onStainless steel
Li metal
Electrolyte
V
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Experimental Results
Chan et. al., Nature Nanotech, 2007
Charge and discharge capacity per cycle
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Experimental Results
Chan et. al., Nature Nanotech, 2007
Charge and discharge capacity per cycleDramatic (~10x) improvement in charging capacity over graphite!
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Experimental Results
Chan et. al., Nature Nanotech, 2007
Charge and discharge capacity per cycleNo decrease in capacity beyond first charge cycle!
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Experimental Results
Cui et. al., Nano Letters, 2009
Core-shell nanowires may improve performance after first cycle
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Experimental Results
Cui et. al., Nano Letters, 2009
Core-shell nanowires may improve performance after first cycleAmorphous shell thickness as a function of growth time
Crystalline core thickness
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Experimental Results
Chan et. al., Nature Nanotech, 2007
Study of reaction dynamics:Near capacity charging at high reaction rates
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Experimental Results
Chan et. al., Nature Nanotech, 2007
Study of reaction dynamics:Near capacity charging at high reaction rates
Even one hour cycle time is much better than a fully charged graphite anode!
Graphite
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Technological Comparison
Li-ion batteries have proved optimal for most mobile electronics and competitive for hybrid and electric vehicles
Technology Power density
Energy density
Lifetime Efficiency
Fuel cells Low/moderate
High Low/moderate
Moderate
Supercapacitors
Very high Low High High
Nanogenerators
Very low Unlimited Unknown Low
Li-ion w/ graphite
Moderate Moderate Moderate High
Li-ion w/ Si NW Moderate High Under investigation
High
Fuel Cells:
Smithsonian Institution, 2008
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Technological Comparison
Li-ion batteries have proved optimal for most mobile electronics and competitive for hybrid and electric vehicles
Technology Power density
Energy density
Lifetime Efficiency
Fuel cells Low/moderate
High Low/moderate
Moderate
Supercapacitors
Very high Low High High
Nanogenerators
Very low Unlimited Unknown Low
Li-ion w/ graphite
Moderate Moderate Moderate High
Li-ion w/ Si NW Moderate High Under investigation
High
Supercapacitors:
Maxwell Technologies, 2009
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Technological Comparison
Li-ion batteries have proved optimal for most mobile electronics and competitive for hybrid and electric vehicles
Technology Power density
Energy density
Lifetime Efficiency
Fuel cells Low/moderate
High Low/moderate
Moderate
Supercapacitors
Very high Low High High
Nanogenerators
Very low Unlimited Unknown Low
Li-ion w/ graphite
Moderate Moderate Moderate High
Li-ion w/ Si NW Moderate High Under investigation
High
Piezoelectric nanogenerators:
Wang, ZL, Adv. Funct. Mater., 2008
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Technological Comparison
Li-ion batteries have proved optimal for most mobile electronics and competitive for hybrid and electric vehicles
Technology Power density
Energy density
Lifetime Efficiency
Fuel cells Low/moderate
High Low/moderate
Moderate
Supercapacitors
Very high Low High High
Nanogenerators
Very low Unlimited Unknown Low
Li-ion w/ graphite
Moderate Moderate Moderate High
Li-ion w/ Si NW Moderate High Under investigation
High
Energy and power density Only fuel cells and batteries can be primary power supply Among those, Si NW batteries are optimal
Lifetime and efficiency Batteries last about as long as typical electronic components Energy efficiency of electrochemical devices is generally high
Market AnalysisFuture OutlookConclusion
Economic Perspective
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Portable Electronics
Lighter Phones
Longer-lasting Laptops
More powerful PDAs
2002 2003 2004 2005 2006 2007 2008 2009 2010 20110
100200300400500600700800900
1000
Worldwide Total Available Market for Portable Rechargeable Electronics
PDAsLaptopsCamcordersDigital camerasMobiles
Year (2008-2011 projected)
Mill
ions
of
Uni
ts
P. Agnolucci, “Economics and market prospects of portable fuel cells”
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Hybrid/Electric Vehicles Emerging market for H/EV batteries Batteries are the main roadblock
Energy density (range) Power density (acceleration)
Li-ion poised to be biggest contender
http://www.chemetalllithium.com/index.php?id=56
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Competing Technologies Other battery technologies
NiMH NiCd other Li-ion
Fuel cells 5/8/09 (CNET News) – “DOE to
slash fuel cell vehicle research” “[...] many years from being
practical.” Portable fuel cells
Supercapacitors <30 Wh/kg Li-ion: <160 Wh/kg
P. Agnolucci, “Economics and market prospects of portable fuel cells”
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Economics of Nanowire Batteries Silicon is abundant and cheap
Leverage extensive silicon production infrastructure
Don’t need high purity (expensive) Si Nanowire growth substrate is also current
collector Leads to simpler/easier battery
design/manufacture (one step synthesis) Nanowire growth is mature and scalable
technique J.-G. Zhang et al., “Large-Scale Production of Si-
Nanowires for Lithium Ion Battery Applications” (Pacific Northwest National Laboratory)
9 sq. mi. factory = batteries for 100,000 cars/day
GM-Volt.com, “Interview with Dr. Cui, Inventor of Silicon Nanowire Lithium-ion Battery Breakthrough”K. Peng et al., "Silicon nanowires for rechargeable lithium-ion battery anodes," Applied Physics Letters, 2008
Can you really get 10x?Si nanowire anode ~3541 Ah/kgAdjust anode/cathode mass ratio
Capacity Issues
J.-M. Tarascon, M. Armand, "Issues and challenges facing rechargeable lithium batteries"
Cathode materialsLithium Cobalt OxideLithium Iron Phosphate
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Lifetime Issues Initial capacity loss after first cycle (17%)
Cause still unknown? Capacity stable at ~3500 Ah/kg for 20
cycles Can’t yet maintain theoretical 4200 Ah/kg
Crystalline-Amorphous Core-Shell Nanowires (2009) Energy Density: ~1000 Ah/kg (3x)
90% retention, 100 cycles Power Density: ~6800 A/kg (20x)
Y. Cui, “High-performance lithium battery anodes using silicon nanowires”Y. Cui, “Crystalline-Amorphous Core-Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes”
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Conclusion Summary
Motivation Technology
landscape Silicon nanowire
battery advantages
Market Prospects
Time to market ~5 years (Cui)