New High-Energy Nanofiber Anode Materials · Electrospinning •Electrospinning is a simple, yet...
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New High-Energy Nanofiber Anode Materials Xiangwu Zhang , Peter Fedkiw, Saad Khan, and Alex Huang North Carolina State University, Raleigh, NC Subcontractor: Jiang Fan American Lithium Energy Corp, San Marcos, CA May 9th, 2011 Project ID # ES010 This presentation does not contain any proprietary, confidential, or otherwise restricted information
Transcript of New High-Energy Nanofiber Anode Materials · Electrospinning •Electrospinning is a simple, yet...
New High-Energy Nanofiber Anode Materials
Xiangwu Zhang, Peter Fedkiw, Saad Khan, and Alex Huang North Carolina State University, Raleigh, NC
Subcontractor:Jiang Fan
American Lithium Energy Corp, San Marcos, CA
May 9th, 2011
Project ID # ES010
This presentation does not contain any proprietary, confidential, or otherwise restricted information
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OverviewTimeline
• Project start date: 09/16/2009 • Project end date: 08/15/2012• Percent complete: 55%
Barriers• Barriers Addressed
– Capacity– Cycle Life– Cost
Budget• Total project funding
– DOE share: $1,349,752 – Contractor share: $1,350,699
Partners• American Lithium Energy
Corp– Jiang Fan – 18650 Cells
• Tec-Cel Inc– Albert Bender– Pilot Production
Relevance:
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Objective• Overall Objective
– Use electrospinning technology to integrate dissimilar materials (lithium alloy and carbon) into novel composite nanofiber anodes, which simultaneously have high energy density, reduced cost, and improved abuse tolerance
• FY11 Objectives– Capacity: At least twice the specific capacity of conventional
graphite electrodes
– Cycle life: 750 cycles of ~70% state of charge swing with less than 20% capacity fade
Relevance:
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MilestonesMonth/Year Milestone or Go/No-Go Decision
August-10 • Establish guidelines for controlling the anode performance by selectively adjusting the processing and structures of the nanofiber anodes
• Assemble, cycle, and evaluate laboratory-scale coin cells• Determine baseline performance of anodes in 18650 cellsGo/No-Go Decision: Achieve initial specific capacities of 650 mAh/g and ~50 full
charge/discharge cycles for nanofiber anodes
August-11 • Fabricate nanofiber anodes that have improved performance• Assemble, cycle, and evaluate 18650 cellsGo/No-Go Decision: Achieve capacity (at least twice the specific capacity of
graphite) and cycle life (750 cycles of ~70% state-of-charge swing with less than 20% capacity fade) for nanofiber anodes
August-12 • Fabricate and deliver nanofiber anodes with specific capacities greater than 1200 mAh/g
• Fabricate and deliver 18650 cellsTarget: Deliver 18650 cells, in which nanofiber anodes have specific capacities
greater than 1200 mAh/g, with cell cycle life longer than 5000 cycles (~70% state-of-charge swing with less than 20% capacity fade)
Approach:
Background (1)
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Silicon Anodes
• Silicon – Extremely high theoretical specific capacity of 4200 mAh g-1
• Challenge – 400% expansion and contraction causes early failures
0 500 1000 1500 2000 2500 3000 35000.0
0.5
1.0
1.5
2.0
Volta
ge (V
)
Capacity (mAh g)
Approach:
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Background (2)Conventional Si/C Anodes
• Si/C anodes – Cycling life can be improved by preparing Si/C composite anodes, but it is still not sufficient for practical applications
• Challenge – To further increase capacity and cycle life simultaneously, a new processing technique must be developed to coat Si with a uniform carbon layer * PVC: polyvinyl chloride
PVC-based carbon-coated Sicomposite anode made byball-milling.
The inset shows the firstcharge-discharge curve of atypical Si anode.
0 5 10 15 20 250
500
1000
1500
0 1000 2000 30000
1
2
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Carbon-coated Si (25 wt %)
Disc
harg
e Ca
pacit
y (m
Ah/g
)
Cycle Number
Si
Pote
ntia
l
(V v
s. L
i/Li+ )
Capacity (mAh/g)
Approach:
Our Approach
• Si nanoparticles are encapsulated in electrospun carbon nanofibers• The nanofiber structure will allow the anode to withstand repeated
cycles of expansion and contraction 7
Electrospun Si/C Nanofibers
Silicon nanoparticle– High Capacity
Carbon nanofiber– Long Cycle Life
Approach:
Electrospinning
• Electrospinning is a simple, yet versatile technique that can produce large quantities of nanofibers with controllable structures
Human hair with electrospun nanofibers in the background
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www.mecc.co.jp
• Production-Scale Machines:
• Current commercial applications:– Freudenberg Nonwovens: air filters,
acoustic nonwovens, and wound pads– Donaldson Company: Ultra-Web®
filters for dust collection– eSpin Technologies: carbon nanofibers
for thermal insulation
Technical Accomplishments and Progress:
Technical Accomplishments and Progress
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1. Preparation and performance of Si/C nanofiber anodes
2. Performance improvement of Si/C nanofiber anodes
3. Scale-up of Si/C nanofiber anodes4. Progress by March 11th
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• Si/C nanofibers were prepared by electrospinning Si + PAN solutions in N,N-dimethylformamide, following by carbonization in Argon
Technical Accomplishments and Progress:
Si + PAN* solution Si/PAN precursor nanofibers
Si/C anode nanofibers
Electrospinning Carbonization
1. Preparation and Performance― Preparation of Si/C Nanofibers
* PAN: Polyacrylonitrile
Technical Accomplishments and Progress:
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Anode: Si/C nanofibers from 15 wt % Si/PAN Electrolyte: 1 M LiPF6 in EC/EMCCurrent density: 100 mA g-1
Si/C nanofibers
Graphite
Cycle Number0 3 6 9 12 15 18 21
1200
1000
800
600
400
Cap
acity
(mA
h g-
1 )
0 200 400 600 800 1000 12000.0
0.5
1.0
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2.0
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3.0
25th 2nd
Volta
ge (V
)
Capacity (mAh g-1)
1st
• Si/C nanofibers have significantly higher capacities than graphite
1. Preparation and Performance― Baseline Performance of Si/C Nanofibers
Technical Accomplishments and Progress:
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2. Performance Improvement
• Improve the anode performance by selectively adjusting the processing and structures of the nanofiber anodes:– Si type, size*, content, and dispersion*– Solution properties: viscosity, surface tension, and conductivity– Spinning conditions: voltage, flow rate, and needle-collector distance– Carbonization conditions: temperature*, time, and heating rate
Technical Accomplishments and Progress:
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2. Performance Improvement― by Changing Si Particle Size
• Nanofiber anodes containing Si nanoparticles (30-50 nm) give the highest capacities
Anode: Si/C nanofibers from 15 wt % Si/PAN Electrolyte: 1 M LiPF6 in EC/EMCCurrent density: 50 mA g-1
0 5 10 15 200
200
400
600
800
1000
1200
1400Di
scha
rge
capa
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(mAh
g-1
)
Cycle number
Si (20 - 30 nm) Si (30 - 50 nm) Si (50 - 70 nm)
Technical Accomplishments and Progress:
14* NaD: Sodium dodecanoateCH3(CH2)10COONa
• The addition of surfactant enhances Si particle dispersion, increases discharge capacity, and improves cycling performance
2. Performance Improvement― by Enhancing Si Dispersion
Si/C nanofibers from 10 wt% Si/PAN
Si/C nanofibers from 10 wt% Si/PAN + 0.1 mol/L NaD* 0 10 20 30 40 50
0
200
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harg
e ca
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Without surfactant With surfactant
Current density: 100 mA g-1
Technical Accomplishments and Progress:
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2. Performance Improvement― by Changing Carbonization Temperature
• Increasing carbonization temperature leads to the formation of more ordered carbon matrix, which is beneficial in improving the anode cycling stability although the discharge capacity decreases
Anode: Si/C nanofibers from 20 wt % Si/PAN Electrolyte: 1 M LiPF6 in EC/EMCCurrent density: 50 mA g-1
XRD of carbon matrix
20 30 40 50 60 70 80 90
900 oC 800 oC
Inte
nsity
( Ar
b. U
nits
)
CuKα 2θ/θ0 5 10 15 20 25
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harg
e ca
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ty (m
Ah g
-1)
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700oC 800oC 900oC
Technical Accomplishments and Progress:
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3. Scale-Up― Lab Scale vs. Production Scale
• Si/C nanofiber anodes produced by production-scale machines have higher capacities than those produced using lab-scale device
Yflow’s eSpinning Unit:
0 5 10 15 200
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Yflow's eSpinning Unit Elmarco's NanospiderTM
Laboratory DeviceDi
scha
rge
capa
city
(mAh
g-1
)
Cycle number
Elmarco’s NanospiderTM:
Laboratory Device:
Anode: Si/C nanofibers from 10 wt % Si/PAN Electrolyte: 1 M LiPF6 in EC/EMCCurrent density: 100 mA g-1
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Technical Accomplishments and Progress:
4. Progress by March 11th― Cycling Performance
0 50 100 150 200 2500
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Capa
city
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apac
ity1
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harg
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• No capacity loss was observed in the first 250 cycles• The test is still ongoing, and the target for FY11 is 750 cycles of
~70% state-of-charge swing with less than 20% capacity fade
• First two cyclesFull charge/discharge (cut-off voltages: 0.05 – 2.5 V)
• Following cycles70% state-of-charge swing, i.e., changing the current polarity if:1) capacity reaches 70% of first-
cycle capacity, or2) voltage reaches cut-off values:
0.05 – 2.5 V
Anode: Si/C nanofibers from 20 wt % Si/PAN Electrolyte: 1 M LiPF6 in EC/EMCCurrent density: 50 mA g-1 Test procedure
Collaborations/Partnerships:
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Collaborations• American Lithium Energy Corp, San Marcos, CA (Industry)
– Jiang Fan, 760-591-0611, [email protected]– The assembling and testing of 18650 cells
• Tec-Cel Inc, Cary, NC (Industry)– Albert bender, 919-878-8464, [email protected] – Licensing the technology– Short-term target: pilot scale production– Longer-term target: full scale production
• Argonne National Laboratory, Argonne, IL (Federal)– Wenquan Lu, 630-252-3704, [email protected]– Improvement of carbon matrix structure by using ANL’s heat-treatment facility
• Indiana University-Purdue University Indianapolis, IN (University)– Jian Xie, 317-274-8850, [email protected] – Improvement of Coulombic efficiency by coating the anodes with graphene or
other materials
Proposed Future Work/Proposed Future Activities:
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• Optimize the anode performance by selectively adjusting the processing and structures of the nanofibers:– Si content, type, size, content, and dispersion (increase capacity and improve
cycle life)– Surface coating using graphene or other materials (increase Coulombic
efficiency)– Solution properties: viscosity, surface tension, and conductivity– Spinning conditions: voltage, flow rate, and needle-collector distance– Carbonization conditions: temperature, time, and heating rate
FY12 Targets:• Anodes: Fabricate nanofiber anodes that have optimized
performance• 18650 cells: Deliver 18650 cells, in which the anode has a specific
capacity greater than 1200 mAh/g and cycle life longer than 5000 cycles of ~70% state of charge swing with less than 20% capacity fade
Future Work
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Summary• Si/C nanofiber anodes have been prepared using the electrospinning
technique• 18650 cells have been assembled using Si/C nanofiber anodes• The performance of Si/C nanofiber anodes has been improved by selectively
adjusting the processing and structures of the nanofibers• The scale-up production is successful, and the resultant Si/C nanofiber
anodes have higher capacities than those produced using lab-scale device• The Year 2 work is still ongoing, and the current results show the FY11
Targets are achievable
FY10 Results FY11 Results(by March 2011)
FY11 Targets (by August 2011)
Capacity ~800 mAh g-1 ~950 mAh g-1Twice the specific
capacity of graphite (i.e., 744 mAh g-1)
Cycle Life50 full
charge/discharge cycles
250 cycles of ~70% state-of-charge swing without capacity fade
750 cycles of ~70% state-of-charge
swing with less than 20% capacity fade
