Sulfur - from hell to powering your car
M. Marinescu
EFL Energy Seminar
June 7th , 2016
Motivation
We need better batteries
Emission reduction policies ⇒ Decrease reliance on carbon fuels
• De-carbonise transport ⇒ xEV
• De-carbonise electrical power grids
Better =
• cheap & long-lasting
• energy & power dense
• light, small
• safe
• versatile
Contestabile, Offer, North, Electric vehicles: a synthesis of the
current literature with a focus on economic and environmental
viability, 2012
Battery requirements
> 95% Li-ion manufacture for consumer electronics
Standard
EV
Cell capacity (Ah)
4
40
Energy density (Wh/kg)
150
150
Life expect (yrs)
3
15
Cell cost ($/kWh)
<250
400
United States Advanced Battery Consortium energy storage system goals, http://www.uscar.org, 2016
From cell to pack
?
35Wh −→ 30 kWh
• structural support
− mechanical vibrations, crash test
• thermal management
− large cells + tight pack of many
• balanced electrically - many cells
Cost of battery pack = double the cost of cells ($800/kWh,
$21000/30kWh)
Attributes for high energy density
1. Large specific capacity of electrodes
Amount of charge they store
2. High Electropotential
Potential difference between anode and cathode
3. Large stoichiometric coefficient
# e- per mole of reactants
4. Low molar mass of active species
Avenues
• Reversibility!
• Mass and volume of non-active materials!
Oxis Energy Ltd
Avenues
P. Bruce, Nat Mat, 2012
Conversion vs intercalation batteries
Intercalation - limited by:
• active material intercalates reversibly
• Li: 1e- , 4V cell (th): 300mAh/g=1200 Wh/kg
Conversion
• active material changes phase reversibly
• many eType
Example
Vcell
Intercalation (now)
LMO
3.8
Intercalation (th)
Wh/kg (th)
Wh/l (th)
550
Wh/kg (max prac)
110-165
1200
240-300
S
LiS
2.2
2567
2200
300-800
M-air
LiO
3.0
3505
3430
700-1000
Reproduced from Cluzel, Douglas, Cost and performance of EV batteries, Element Energy report for The comittee
on climate change, 2012
Why LiS
• gravimetric energy density 3
• safety (*) 3
• cheap 3
• low temperature performance 3
http://www.shorpy.com/
• power density (discharge rate) 7
• cycle life 7
• volumetric energy density 7
* Hunt, Patel, Szczygielski, Kabacik, Offer, Journal of Energy
Storage 2, 2015
LiS in use
www.airbusgroup.com/int/en/story-overview/
http://www.oxisenergy.com/applications/
• lightweight
• safe
• low operating T
https://protonex.com/blog/what-do-soldiers-carry-and-whats-
LiS operation
Discharge
LiS operation
Charge
LiS operation
Effect of current
LiS operation
Effect of current
LiS challenges
• improve rate capacity
• improve cycle life
- capture poly-S in cathode
- ensure homogeneous Li plating on anode
- design cathode microstructure
• improve SOC estimation
Manthiram et al, Acc Chem Res 46, 2012
Improving performance and use of LiS through modelling
REVB: Revolutionary Electric Vehicle Battery
• Target: 400Wh/kg LiS cells
• Physics-based models & reduced-order models
• Battery pack design, drive-cycle testing
Funded by EPSRC and Innovate UK
0D model formulation
S8 0 + 4 e− ←−→ 2 S4 2−
S4 2− + 4 e− ←−→ 2 S2− ↓ + S2 2−
0D model formulation
I = iH + iL
IL
V = (E + η)cathode −(E + η)anode
−
|
{z
} | {z } κA
Vcathode
Vanode

• species formed/destroyed by e-chemical reactions 


• shuttle = S80 → S42− without e-
• precipitation model with nucleation



• Nernst equations: equilibrium potential of reactions
• Butler Volmer approximation: reaction currents
dSn
dt
Species evolution during operation
• Can track charge status of battery
• Qualitative charge/discharge voltage curves retrieved without
need of differing mechanism
Precipitation during discharge
2.4
EL =
EL0
+
RT
4F
ln
S 2−
cL (S 2−4)2 S 2−
2
Potential (V)
2.35
[S 2(g), k
*
2.3
p
(s -1 )] =
no ppt
0.0001, 100
0.0050, 100
0.0001, 500
0.0050, 500
2.25
2.2
2.15
2.1
0
0.5
1
1.5
2
2.5
Discharge capacity (Ah)
Flat voltage plateau during discharge is caused by precipitation.
Zhang, Marinescu, O’Neill, Wild, Offer, Phys. Chem. Chem, Phys. 17, 2015
Marinescu, Zhang, Offer, Phys. Chem. Chem. Phys 18, 2016
3
3.5
Charging rate
Limited by shuttle and precipitation
• fast charge ⇒ ’slow’ dissolution
• slow charge ⇒ shuttle
Limitations of 0D model
No mass transport
⇒ mass transport in 1D model
1D model formulation
• PDE’s species conc
• flux of species mass
• diffusion and
migration
Kumaresan, Mikhaylik, White, J. Electrochem. Soc. 155, 2008
Ghaznavi & Chen, J. Power Sources 257, 2014
1D model predictions
Discharge rate retrieved for slow Li+ diffusion
T. Zhang, M. Marinescu, S. Walus, G. J. Offer, submitted, 2016
1D model predictions
Capacity recovery retrieved for slow Li+ diffusion
T. Zhang, M. Marinescu, S. Walus, G. J. Offer, submitted, 2016
What we learnt from modelling
Models show
• precipitation/dissolution limits charge rate
• transport through separator limits discharge rate
• ’recent history’ effect:
• accumulated precipitate
• concentration gradients in electrolyte
• crucial for SOC estimation
Current work:
• degradation: irreversible vs reversible loss
• thermal coupling
Predictions
Time to market
Chemistry
1st paper/patent
1st commercial cell
1st use series car
LCO
1979
1991
2008 (Tesla)
LMO
1983
1996
2009 (iMieV)
LFP
1994
2006
2007 (MODEC van)
Ni-MH
1967
1990
1997 (Prius)
Reproduced from Cluzel, Douglas, Cost and performance of EV batteries, Element Energy report for The comittee
on climate change, 2012
Conclusions
Chemistry in car in 10 yrs?
• Companies scaling up now
• Only incremental increase
When step change increase?
• Current status = Nature paper
• Step change → 20 yrs
Application targeted chemistry?
• high energy vs high power
• numbers are driven by behaviour
Extra slides
0D model formulation
Species evolution
dS80
dt
= −nS8 aiH − ks S80
dS42−
dt
= nS8 aiH + (1 − fl
dS22−
dt
= nS2 aiL
1
kp Sp S 2− − S∗2−
= 2nS aiL −
vρS
1
=
kp Sp S 2− − S∗2−
vρS
MS8
= ks S80 ,
a=−
ne F
dS 2−
dt
dSp
dt
dSs
dt
Ss
)ks S80 − nS4 aiL
mS
0D model formulation
Reaction equilibrium and kinetics
S8 0 + 4 e− ←−→ 2 S4 2−
S4 2− + 4 e− ←−→ 2 S2− ↓ + S2 2−
Nernst equation for equilibrium potential
!
RT
S80
0
EH = EH
+
ln cH 2−
4F
(S4 )2
!
RT
S42−
0
EL = EL +
ln cL 2− 2 2−
4F
(S ) S2
Butler-Volmer approximation for reaction current
ne F ηH
,
2RT
ne F ηL
iL = 2iL,0 ar sinh
.
2RT
iH = 2iH,0 ar sinh
ηH = V − EH
ηL = V − EL
I = iH + iL
V = (E + η)cathode −(E + η)anode
−
|
{z
} | {z }
Vcathode
Vanode
IL
κA
Definitions from 0D model
n2S4 MS8 v
,
nS8
2 v2
n2 nS2 MS8
cL = S
,
nS4
cH =
(1a)
(1b)