a virtual li/s battery: modeling, simulation and computer-aided development david n. fronczek 1,2,3...
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A virtual Li/S battery: Modeling, simulation and computer-aided development
David N. Fronczek1,2,3 and Wolfgang G. Bessler1,2,4
1German Aerospace Center (DLR) 2Helmholtz Institute Ulm (HIU)3Lawrence Berkeley National Laboratory (LBNL)4From 09/2012: Offenburg University of Applied Sciences
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Introduction
• Fundamentals of Li/S batteries
• Modeling approach
• Simulation results
• Outlook & Summary
www.DLR.de • Chart 2
DLR – The German Aerospace Center
Locations and employees
- ~8000 employees across 33 institutes and facilities at13 sites.
- Offices in Brussels, Paris and Washington.
- DLR Institute of Technical Thermodynamics: R&D activity of Electrochemical Energy Technology since 1986
n Cologne
n Oberpfaffenhofen
Braunschweig n
n Göttingen
Berlin n
n Bonn
n Neustrelitz
Weilheim n
Bremen n n Trauen
n Dortmund
Lampoldshausen n
Hamburg n
Stuttgart n
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 3
http://www.dlr.de/tt/en/
Electrochemical Energy Technology
Head: Prof. K. Andreas Friedrich
PersonnelAbout 60 employees 5 research areas
- SOFC – Günter Schiller - PEFC – Erich Gülzow - Batteries – Norbert Wagner- Modeling – Wolfgang Bessler- Electrochemical systems – Josef Kallo
Budget 2011~ 8 M€ (without operation cost of large test facilities)About 50 % third-party funding
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 4
Modeling and simulation of lithium batteries
LiFePO4 batteries:Electrochemistry and impedance
Li+e–
-Understanding and optimization of physicochemical behavior
Thermal management and runaway risk
-Understanding and optimization of thermal and safety behavior
Lithium-sulfur cells:Redox chemistry and transport
-Analysis of cycling propertiesand chemical reversibility
Lithium-air cells:Multi-phase chemistry and reversibility
- Improvement of porous air electrode
Lithium-ion technology Post lithium-ion cells
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 5
Helmholtz Institute Ulm forElectrochemical Energy Storage
• Center of Excellence for research in electrochemical energy storage
• Started in Jan. 2011
• New building on University Ulm campusfor 80 scientists (2013)
• DLR battery modeling activities are integrated into HIU
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 6
http://www.hiu.kit.edu/
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Introduction
• Fundamentals of Li/S batteries
• Modeling approach
• Simulation results
• Outlook & Summary
www.DLR.de • Chart 7
www.DLR.de • Chart 8 > Lithium/Sulfur Batteries: An Elementary Modeling Approach > D. N. Fronczek • ModVal 9 > April 2, 2012
Lithium/sulfur batteries – properties and potentials
Li-Ionhigh E
Pb Li-Ionhigh P
Li/S Li-air
10 100 1000 10000
Specific energy / Wh/kg
gasoline(50 % of theoretical max.)
10 100 1 000 10 000Specific Energy / Wh/kg
Y. Mikhaylik et al., Sion Power Corp., ECS presentation, 2009.
USABC targetsLi/S (2009)
Rate Cap.
Lower T
Power Density
Specific Power
Recharge Time
Specific Energy
Energy density
Upper T
Cycle life
www.DLR.de • Chart 9> Lithium/Sulfur Batteries: An Elementary Modeling Approach > D. N. Fronczek • ModVal 9 > April 2, 2012
Lithium/sulfur battery – layout
Global reaction: S8 + 16 Li 8 Li⇄ 2S + 3400 kJ/mol
Complex chemistry, complex multi-phase behavior!
PositiveElectrode
Negative ElectrodeSeparator
Lithium(metal)
Sulfur / Carbon matrix Organic Electrolyte
Li+ Li0
Dis
ch
arg
e
Ch
arg
e
S8
Li2S8
Li2S4
Li2S2
Li2S
S82−
S62−
S42−
S22−
S2−
Li2S6
Cur
rent
col
lect
or
Cur
rent
col
lect
or
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Introduction
• Fundamentals of Li/S batteries
• Modeling approach
• Simulation results
• Outlook & Summary
www.DLR.de • Chart 10
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Computational domain
• Modeling framework: DENIS (detailed electrochemistry and numerical impedance simulation)*
• 1D continuum model, 15 mesh points
• 169 algebraic and differential equations (standard model)
y
PositiveElectrode
Separator NegativeElectrode
www.DLR.de • Chart 11
*W. G. Bessler, S. Gewies, M. Vogler, A new framework for physically based modeling of solid oxide fuel cells, Electrochimica Acta 53 (2007) 1782-1800.
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Governing equations
• Electrochemistry (evaluated by CANTERA†):
Rates of production and relation to current
Modified Arrhenius rate expressions
• Transport in the liquid electrolyte: diluted solution theory
Nernst-Planck-eq.
†D. G. Goodwin et al., Cantera, http://code.google.com/p/cantera, 2001-2012.
www.DLR.de • Chart 12
Governing equations
• Evolution of Phases‡
Production rate derived from chemical source terms
Adaptive active surfaces ( : volume fraction)
• Plus boundary conditions, e.g. electroneutrality
www.DLR.de • Chart 13> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
‡J. P. Neidhardt, D. N. Fronczek, T. Jahnke, T. Danner, B. Horstmann, and W. G. Bessler, "A flexible framework for modeling multiple solid, liquid and gaseous phases in batteries and fuel cells," J. Electrochem. Soc., in press (2012)
Electrochemical model
Chemical reactions considered on the positive electrode side:
sulfur reduction precipitationS8(s) ⇌ S8(l)
S8(l) + 2 e− ⇌ S82− 2 Li+ + S8
2− ⇌Li2S8(s)
S82− + 2⁄3 e− ⇌ 4⁄3 S6
2− 2 Li+ + S62− ⇌
Li2S6(s)
S62− + e− ⇌ 3⁄2 S4
2− 2 Li+ + S42− ⇌ Li2S4(s)
S42− + 2 e− ⇌ 2 S2
2− 2 Li+ + S22− ⇌
Li2S2(s)
S22− + 2 e− ⇌ 2 S2− 2 Li+ + S2− ⇌
Li2S(s)
Lithium plating/stripping on the negative electrode side:
Li(s) Li⇌ + + e−
Global reaction: 16 Li + S8 8 Li⇌ 2S + 3400 kJ/mol, EMF = ~2.2 V
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 14
* K. Kumaresan, Y. Mikhaylik and R. E. White, J. Electrochem. Soc. 155, A576 (2008)
Lis
t o
f p
aram
eter
s
www.DLR.de • Chart 15> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Introduction
• Fundamentals of Li/S batteries
• Modeling approach
• Simulation results
• Outlook & Summary
www.DLR.de • Chart 16
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Simulated experiment
• CC discharge, CCCV charge @ ~1/50 C
0 50 100 150 200
-0.4
-0.2
0.0
0.2
0.4
Time / h
C
urre
nt d
ensi
ty /
A/m
2
0
400
800
1200
1600
2000
Cap
acity
/
Ah/
kgS
ulfu
r
www.DLR.de • Chart 17
www.DLR.de • Chart 18> Lithium/Sulfur Batteries: An Elementary Modeling Approach > D. N. Fronczek • ModVal 9 > April 2, 2012
Results: Discharge / charge profile
• Two distinct stages during discharge can be reproduced
• Explanation: Presence of solid S8 (Phase I) or Li2S (Phase II)
• CV charge phase
necessary to re-
cover full capacity
• Asymmetric phase
behavior during
charge/discharge
0 50 100 1502.0
2.2
2.4
2.6
2.8
Time / h
Ce
ll vo
ltag
e /
V
0.0
0.1
0.2
0.3
0.4
0.5
Li2S
Vol
ume
frac
tion
S8(s)
Results: Discharge / charge profilecompared to experiment
Experiment Simulation
www.DLR.de • Chart 19> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
0 400 800 1200 16001.5
2.0
2.5
Discharge capacity / Ah/kgSulfur
Cel
l vol
tage
/ V
0 400 800 1200 16001.8
2.0
2.2
2.4
2.6 0.01C 0.1C 1C
Cel
l vol
tage
/ V
Discharge capacity / Ah/kg of S8
*N. Cañas, K. Hirose, N. Wagner, Ş. Sörgel and K. A. Friedrich, "In-situ XRD and electrochemical characterization of cathodes for Li-sulfur batteries“, 2nd Ertl Symposium on Surface and Interface Chemistry, June 24–27 2012, Stuttgart, Germany, Poster.
Results: Cathode composition
• The composition of the cathode varies tremendously during discharge and charge, as phases are formed and consumed
• Discharge and charge are asym-metric processes, introducing hyster-esis into the system
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 20
0 50 100 150 200
Vol
ume
frac
tion
Time / h
Carbon
Sulfur
Li2S
Electrolyte
0.4
0.2
0.0
1.0Discharge CC charge CV charge
0.5
Results: Cathode compositioncompared to experiment
www.DLR.de • Chart 21> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
*N. Cañas, K. Hirose, N. Wagner, Ş. Sörgel and K. A. Friedrich, "In-situ XRD and electrochemical characterization of cathodes for Li-sulfur batteries“, 2nd Ertl Symposium on Surface and Interface Chemistry, June 24–27 2012, Stuttgart, Germany, Poster.
Li2S [2 2 2]
S8 [2 2 2]
- *
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Results: Concentrations
• Species concen-trations are highly time and SOC dependant
• S8 and S2− concen-trations buffered by presence of solid phases
• Current breaks down when electrolyte is depleted of (Poly-) sulfide ions
0 50 100 15010-9
10-6
10-3
100
103
Time / h
Con
cent
ratio
ns /
mol
/l
Li+
S2-
S8(l)
S2-4
S2-6
PF-6
S2-2
S2-8
Discharge ← → Charge
www.DLR.de • Chart 22
0 100 200 300 4000
100
200
300
400
Im /
Ohm
*cm
2
Re / Ohm*cm2
100 % 99 % 75 % 50 % 25 % 3 %
Results: Impedance
• EIS simulation based on
physicochemical model
(no equivalent circuit)*
• Non-ambivalent
interpretation of results
• Cell performs best when
discharged!
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 23
*W. G. Bessler, "Rapid impedance modeling via potential step and current relaxation simulations," J. Electrochem. Soc. 154, B1186-B1191
0 100 200 300 4000
100
200
300
400
Im /
Ohm
*cm
2
Re / Ohm*cm2
100 % 99 % 75 % 50 % 25 % 3 %
Results: Impedancecompared to experiment
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 24
*W. G. Bessler, "Rapid impedance modeling via potential step and current relaxation simulations," J. Electrochem. Soc. 154, B1186-B1191
Experiment Simulation
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Introduction
• Fundamentals of Li/S batteries
• Modeling approach
• Simulation results
• Outlook & Summary
www.DLR.de • Chart 25
Outlook
Li/S trends:
• Higher sulfur contents
• Engineered nanostructured
materials
• Profound understanding is
paramount to successful
electrode/cell design
www.DLR.de • Chart 26> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
*E. J. Cairns, " Beyond Lithium Ion: The Lithium/Sulfur Cell “, Beyond Lithium Ion V Meeting,June 5–7, 2012, Berkeley, CA
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Summary
• Li/S model implemented in multi-phase framework
• Prediction of- voltage, current and capacity- concentrations- porosity and volume fractions
• Qualitative explanation of- two distinct stages during discharge- electrochemical impedance
• Toolset established for further investigations,
e.g. of degradation mechanisms
Li
S
0 500 1000 1500
Discharge capacity / Ah/kgSulfur
Ce
ll vo
ltag
e
/ V
Vo
lum
e f
ract
ion
S8Li2S
0.5
0.0
0.25
2.5
2.4
2.3
www.DLR.de • Chart 27
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
A virtual Li/S battery: Modeling, simulation and computer-aided development
• Appendix
www.DLR.de • Chart 28
Multi-scale modeling of electrochemical systems
- Knowledge-based advancement of fuel cells and batteries at DLR using multi-scale and multi-physics modeling and simulation methods
- Head: Wolfgang G. Bessler. Group: ~10 scientists and PhD students
www.DLR.de • Chart 29> Lithium/Sulfur Batteries: An Elementary Modeling Approach > D. N. Fronczek • ModVal 9 > April 2, 2012
Lis
t o
f eq
uat
ion
s
www.DLR.de • Chart 30> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 •
Results: Transport in the Li/S cell
• The sulfur content in the porous cathode changes significantly and non-uniformly
during discharge and charge
• Sulfur is redistributed in the cell
> A virtual Li/S battery: Modeling, simulation and computer-aided development > D. N. Fronczek > Next Generation Batteries 2012 > July 19, 2012 • www.DLR.de • Chart 31