high capacity composite carbon anodes - energy.gov · sem sem liu h.k. electrochem. solid state...
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High Capacity Composite Carbon Anodes
PI: Vilas G. Pol Chemical Sciences and Engineering Division, Argonne
Annual Merit Review
DOE Vehicle Technologies Program
Arlington, VA May 14-18, 2012
ES114
This presentation does not contain any proprietary, confidential, or otherwise restricted information Vehicle Technologies Program
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Overview
Timeline Start date: FY11 End date: FY14 Percent complete: On-going project
Budget
Total project funding: - 100% DOE FY11: $300K FY12: $300K
Barriers Addressed
Cost Abuse tolerance limitations
Partners
Co-investigators: M. Thackeray (Co-PI) Collaborators:
- M. Ewen, Z. Mao (ConocoPhillips) - J. Ayala, F. Henry (Superior Graphite) - L. Curtiss, K. C. Lau (EFRC-CEES)
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The objective of this project is to evaluate spherically-shaped carbon anode materials, particularly when combined with lithium-alloying elements (e.g., Sn, Sb) to produce high-capacity carbon-metal composite anodes for HEVs, PHEVs and Evs, and to compare their electrochemical behavior with commercial carbon materials in collaboration with industry.
Objective
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Milestones (FY12)
Consolidate industrial collaborations for this project
Prepare carbon samples for industrial partner for heat-treatment; prepare carbon-composite samples from Argonne’s carbon materials and from industrial products
Evaluate and optimize the electrochemical properties of carbon-composite samples in lithium half cells and full cells
Determine the chemical, physical and thermal properties of Argonne’s carbon-composite anodes with commercial carbon-composite materials
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Approach
Exploit autogenic reactions to prepare spherical carbon quickly, cost effectively and reliably Collaborate with industry to access high-temperature furnaces to increase the graphitic component in spherical carbon Increase the capacity of the carbon spheres by combining them with lithium alloying elements to form carbon-composite anode materials Study and compare the electrochemical, chemical, physical and thermal properties of Argonne’s carbon-composite products with commercially available carbon materials Optimize processing conditions and evaluate the electrochemical properties of pristine and carbon-composite materials
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Mesocarbon microbeads (MCMB)
2µm
Argonne’s carbon spheres (SCPs)
Why Spherical Carbon Particles (SCPs) as an Anode?
SEM SEM
Liu H.K. Electrochem. Solid State Lett. 7, A250, 2004 Pol V.G. Environmental Sci. & Tech. 2010, 44, 4753
SCPs provide sloping voltage profile similar to hard carbon – safer than graphite SCPs offer the possibility of smoothing the current distribution at the carbon
electrode surface during charge, thereby reducing the risk of lithium dendrites
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Autogenic Reactions: Self-generating reactions that occur within an enclosed vessel, typically at high pressure and temperature
Precursor(s) Critical Phase Product
HEAT COOL
Autogenic Synthesis of Spherical Carbon Particles
Single step, efficient process
Solvent-, catalyst free
Produces pure products
Proceeds at moderate temp.
Advantages
80 cc Cap.
2000 PSI
800 oC
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10µm10µm
1µm1µm
HDPE
700 0C/1min.
490 PSI
‘Upcycling’ of Carbon Waste
Solid, dense, micron sized spherical carbon particles with smooth surfaces Can also be prepared from C9H12, Naphthalene, hexane, ethanol etc.
1µm1µmSolid nature
Industrial implications 8
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First cycle capacity loss ~60%, steady cycling for hundreds of cycles
As-prepared SCPs (700oC) collapse during lithiation and delithiation
Electrochemistry of Li/SCP Cells
SCP:acetylene black: PVDF ratio = 85:8:7
1.2M LiPF6 in EC:DMC
~1C rate
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10µm 1µm
Jorge Ayala and Francois Henry
Morphology of SCPs is preserved after heat treatment (still solid and dense)
Graphitic order is improved in SCP-HT24 particles
High Temperature Treatment of SCPs (2400 oC/1h/Ar)
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25% first cycle capacity loss, sloping potential profile, steady cycling
>99% coulombic efficiency , heat-treated SCPs remain intact during cycling
Electrochemistry of Li/SCP-2400 °C Cells
(I = 235mA/g)
5µm
1µm
SEM cycled electrode
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Particle sintering
Morphology of SCPs is maintained at 2800 oC
Dense, solid particles with smooth surfaces
Sintering of particles is observed
10µm 1µm
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High Temperature Treatment of SCPs (2800 oC/1h/Ar)
Mark Ewen and Zhenhua Mao
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Electrochemistry of Li/SCP-2800°C Cells
(I = 235mA/g)
15% first cycle capacity loss, several break in cycles required
>99% coulombic efficiency, steady cycling 13
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Structural and Morphological Studies – Cycled Electrodes
No significant changes in the spherical shape of SCP-2400 oC particles (200 cycles)
Local strain induced and graphitic character decreases within the SCPs during electrochemical cycling
5µm
5µm
uncycled
cycled
G G' D D' Raman spectra SEM images
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A Comparison: SCP vs. MCMB Electrochemical performance
D
G
0.12
ID/IG
0.35
MCMB
SCP
Raman Spectra
Sloping behavior of hard carbon
Initial several break in cycles were required for both types of carbon
SCPs behave like a hard carbon unlike the graphitic character of MCMBs
I=235mA/g
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First-cycle capacity loss = 28% (cell balancing is required)
Specific capacity of cathode: ∼160 mAh/g
Li-Ion Full Cell: SCP/High Capacity LMR-NMC (LMR-NMC = 0.5Li2MnO3•0.5LiNi0.44Mn0.31Co0.25O2)
Rate ∼C/3
Courtesy: Donghan Kim, ANL 16
1st charge 2nd charge
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SCP electrodes generate less heat than natural graphite (NG) on reaction with the electrolyte between 100-200 °C.
0
4
8
50 100 150 200 250 300 350
Temperature (0C)
Hea
t Flo
w (W
g-1)
Carbon spheres
Electrolyte decomposition at the graphite surface
NG
Lee, et al. Adv. Mater. 22, 2172 (2010)
380J/g
1µm1µm
SEI Breakdown*
Heat generation during SEI breakdown – DSC data
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*1960 J/g reported for flaky graphite (ANL Report-03/16 2003)
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Structural evolution of carbon spheres
Heated SCPs are significantly more crystalline than the as-prepared spheres, as reflected by an increase in the (002) XRD peak intensity
A decrease in the ID/IG ratio (Raman data) confirms the increase in the graphitic character of the carbon spheres 18
1.1
0.46
0.35
ID/IG ratio
(002) XRD Raman
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SCP + SnCl2 SCP + SnO2 SCP
Sonication SCP-2400 °C + Sn precursor in organic solvent )))))) → SnO2@SCP nanoparticles
SCPs are thinly and uniformly coated (elemental mapping) by Sn precursor
Heat treatment (500 °C/Ar) turns Sn precursor into <10 nm SnO2 crystallites
Increasing the capacity of SCP by SnO2 deposition
500 oC/ Ar
C surface
SnO2
SnO2
HR-SEM TEM HR-TEM
SEM SEM SEM
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Capacity vs Cycle No. Plot: Li/SnO2-SCP(2400 °C) Cell
SnO2-coated SCP electrodes deliver significantly higher capacity than pure SCPs (340 mAh/g at a C/2.7 rate vs. ∼250 mAh/g for SCP-2400 °C)
Very stable cycling Implications for further improvement (Sn coatings) and industry carbons.
D
C
340 mAh/g
(I=136 mA/g, 1.5 - 0.01V, SCP + 10wt.% Sn)
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Metallic Sn nanoparticles were successfully decorated on the surface of industrial graphite particles.
The presence and uniform distribution of Sn was confirmed by XRD, EDS and elemental X-ray dot mapping
Graphite
Graphite + Sn
Graphite + Sn (200 °C)
XRD patterns: C6 + tetragonal Sn
Industry Graphite/Sn Composite Anodes Source: ConocoPhillips
Elemental X-ray mapping
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0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 200 400 600
Volta
ge (V
)
Capacity (mAh/g)
ConocoPhillips graphite/Sn
Charge 1Discharge 1Charge 2Discharge 2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 100 200 300
Volta
ge (V
)
Capacity (mAh/g)
ConocoPhillips graphite
Charge 1Discharge 1Charge 2Discharge 2
0
100
200
300
400
500
0 5 10 15 20 25 30
Cap
acity
(mA
h/g)
Cycle Number
CC-G8
DC-G8
I=100mA/g (~ C/3) rate
Graphite Graphite + Sn
Capacity vs. Cycle No.
Electrochemical data of industry graphite and C6/Sn
Industry graphite intercalates lithium below 0.2 V, while the Sn component provides additional capacity by alloying with Sn at ∼0.4 V vs. Li0.
Work is in progress to stabilize the cycling capacity of graphite/Sn composite electrodes (cf. SCP/Sn) – e.g., manipulating sonication process to improve binding of Sn to graphite
At moderate rate (∼C/3), the graphite/Sn composite electrode initially provides higher capacity than bare graphite (∼10 cycles)
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Optimize autogenic reaction parameters to improve electrochemical capacity of spherical carbon particles and other rounded shapes
Fabricate smaller carbon spheres (<1µm)
Further increase the electrochemical capacity of the carbon spheres by combining the spheres with a lithium-alloying component (Si, Sn and Sb), e.g., by sonication
Extend processing studies to fabricate high-capacity carbon-composite anode materials using commercially available carbon products
Extend electrochemical studies to include full cell evaluations
Future Work - FY2012/FY2013
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Spherical carbon particles were prepared by autogenic reactions, maintaining their morphology after high temperature treatment with improved graphitic character.
Spherical carbon behaves electrochemically like a hard carbon, delivering approximately 250 mAh/g when cycled between 1.5 V and 5 mV vs. Li0. High temperature treatment at 2400 °C under inert conditions increases the graphitic character of the carbon spheres and significantly reduces the first cycle capacity loss from 60% (700 °C preparation) to 15% (SCP-HT/1h).
Higher heat treatment (2800 C) does not significantly increase the capacity of the carbon spheres.
The electrochemical capacity of the carbon spheres can be significantly increased by decorating the surface with ∼10 wt.% Sn nanoparticles.
Very stable cycling capacity is achieved. Efforts to increase the anode capacity of industrial carbon/Sn composites well above the
theoretical value for graphite using the same surface coating techniques are underway.
Summary
Support for this work from Peter Faguy and David Howell of DOE-EERE, Office of Vehicle Technologies, is gratefully acknowledged. Superior Graphite and ConocoPhillips are thanked for the high-temperature treatment of the carbon spheres and for providing graphite samples.
Acknowledgements
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