Transcript Materials Team Dialogue / Review with PNGV Directors Sept

Electrochemical and thermal
characterization of Li-ion batteries
Jai Prakash
Center for Electrochemical Science and Engineering
Department of Chemical and Biological Engineering
Illinois Institute of Technology
CESE
November 13, 2009
Metal oxide cathode
LiMO2
Oxide
LiPF6/EC,DMC
Li-ion cell reactions
Graphite anode
MCMB
1 m
2 m
High volumetric energy/power densities
CESE
November 13, 2009
Limitations of Li-ion cells
High power performance
Cell impedance)
Cycle life
Cell impedance
Thermal safety
Structural stability of delithiated oxide
Cell impedance produces heat
Cost
CESE
November 13, 2009
Typical Changes in Li-ion Cell EIS with Time
EIS for G2.60C55.A215.33.28.26.G.T.
0.03
Characterization t = 0
RPT #1 t = 4 weeks
0.025
RPT #2 t = 8 weeks
RPT #3 t = 12 weeks
RPT #4 t = 16 weeks
-Zimag, ohms
0.02
RPT #5 t = 20 weeks
RPT #6 t = 24 weeks
mid-freq min
RPT #7 t = 28 weeks
0.015
RPT #8 t = 32 weeks
RPT #9 t = 36 weeks
high freq min
0.01
0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Zreal, ohms
Impedance rise is associated with interfacial arc
Most of the impedance is attributed to the positive electrode
CESE
November 13, 2009
0.04
HR-TEM of cycled oxide particles
~ 5-10 nm
LixNi1-xO-type
5 nm
Surface
Film
LiNiO2-type
(003) reflections are weak or absent
in oxide surface layers
CESE
November 13, 2009
Electrochemical Model Approach
 Porous electrode model
 Solid electrolyte interface (SEI) and interfacial oxide film
included in the model
 Diffusion through the electrolyte, SEI film, interfacial
oxide, and bulk oxide considered
 Butler-Volmer relation used for electrochemical reaction
 AC impedance model constructed for Li-ion cell
CESE
November 13, 2009
Governing equations for the AC impedance model
c  c0  c  c0  c ' e jt  c0  (cR  jcI )e jt
Linear perturbation
complex analysis
D  D
c c0
 dD

 dc
c c0

c 

Kinetic impedance and lithium diffusion in active particles
 a  a 
F
RT




2
2
 o (a  a ) F 
k
   cm 
RT


ko 
Znk
j
 cm
2
 o (a  a ) F 
2
k
  ( cm )

RT

dU b   1  K Dsb tanh   j  tanh   j  

 b

 i

s
 - K s dc

D
D
D
si
si  
sb 


sb

Zs  



 z F Dsi j  
Dsb
j 
j  
tanh   b

 Ks
  tanh   i





D
D
D
si
si  
sb 



Numerical solution of a set of coupled differential equations
CESE
November 13, 2009
Simulation and prediction for the positive electrode
-Z" (Im) Ohm.cm2
Oxide layer
simulation
20
Experimental
15
20 nm oxide layer
20
10 nm oxide layer
10
0
10
0
5
5
10
15
20
4
8
Z' (Real) ohm.cm 2
12
Particle size
0
0
5
10
15
20
Z' (Real) ohm.cm2
25
-Z" (Im) ohm.cm
2
Z" (Im) ohm.cm2
25
30
6
5
4
3
2
1
0
4.00 m
1.55 m
0.37 m
0
CESE
November 13, 2009
Safety Concerns of Li-ion Batteries
• Large-scale batteries for electric and hybrid
vehicles
• Thermal runaway
-High power discharge
-Overcharge
-Abusive and cell-shorting conditions
• Heat and pressure build-up within the cell
• Cell fire caused by the flammable electrolyte
CESE
November 13, 2009
Thermal runaway produces fire in Li-ion cells
Peter Roth (Sandia National Lab)
18650 Li-ion cell
CESE
November 13, 2009
Understanding Thermal Runaway in Li-ion Cells:
A Fire Triangle
CESE
November 13, 2009
In-situ studies of thermal effects in Li-ion cells
during normal cycling using IMC
70
Current
C/20
C/10
C/5
C/1
Qanode
61
54
27
-74
-84
-93
-110
-214
60
Charge
Heat Rate, uW.cm -2
50
40
30
mJ.cm-2
20
10
0
Qcathode
-10
mJ.cm-2
Discharge
-20
-30
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
x in Li xNi0.8Co0.15Al0.05O2
CESE
November 13, 2009
DSC features of Mag-10 anode at various SOC
-17
Normalized Heat Rate, W/g
-15
-13
-11
Li0.9C6
-9
Li0.7C6
-7
Li0.57C6
-5
-3
Li0.37C6
Li0.18C6
-1
Li0C6
1
60
110
160
210
260
Temperature, oC
CESE
November 13, 2009
310
360
Enthalpy vs. the amount of intercalated lithium in
the secondary SEI film formation
-3000
-2500
1600 J/g for Mag-10
delta_H, J/g
-2000
-1500
-1000
The formation of a secondary
SEI film consumes about 0.37 Li
-500
0
0
0.2
0.4
0.6
x in LixC6
CESE
November 13, 2009
0.8
1
DSC and XRD of LiNi0.8Co0.15Al0.5O2 cathode at various SOC
8
Peak shift
7
6
H (J/g)
5
100%
4
70%
3
- 941 J/g
- 730 J/g
50% - 709 J/g
2
20% - 352 J/g
1
0%
0
- 150 J/g
200
250
300
350
Temperature, o C
113
150
018
100
110
5000
50
107
Normalized Heat Flow (exo up), W/g
9
Intensity, counts
4000
250o C
3000
225o C
200o C
2000
175o C
o
150 C
1000
100o C
25 oC
0
55
CESE
Li2O +NiO + Co3O4 + Al2O3 + O2
→
Li0.36Ni0.8Co0.15 Al0.05O2
November 13, 2009
60
65
Angle, 2
70
75
Thermal studies of Li0.36Ni0.8Co0.15Al0.05O2 (CDL) With and
Without Electrolyte using ARC
300
Temperature, oC
250
Flash point of EC:
150oC
200
SHR dramatically
increased from
150oC is due to the
combustion of the
electolyte with
released O2 from
delithiated cathode
150
100
Electrolyte
CDL w/o electrolyte
CDL w/electrolyte
CDL w/all components
50
0
0
500
1000
1500
2000
Time, min
CESE
November 13, 2009
2500
3000
A conceptual road map for the thermal runaway
in Li-ion cells
High Rate
T> 85o C
T > 140o C
Abusive Conditions
Internal Shorts
Anode SEI/Elect.
 H = 350 J/g
Solvent/Salt
 H = 200 J/g
Cathode SEI/Elect.
 H = 300 J/g
T > 180o C
LiNi0.8 Co0.2 O2 /Elect.
 H = 500 J/g
T > 200o C
Lix C6 /PVDF/O2 /Elect.
 H = 1500 J/g
T > 660o C
CESE
Stable SEI films
Need stable cathode
O2 Evolution
Fire
Aluminum Meltdown
H = - 395J/g
November 13, 2009
Need nonflammable
electrolytes
Approaches to improve thermal safety of Li-ion cells
 Use of additives to form stable SEI film
» Stable SEI film decomposes at higher temperature
» Avoids the secondary SEI formation
» Delay the initiation of thermal runaway
 Thermally stable cathodes
» Stable spinel oxides
» Core-shell cathodes (Hanyang university)
 Nonflammable electrolytes
» Flame retardant additives
» Nonflammable solvents
CESE
November 13, 2009
Effects of VC, VEC and LiBOB additives on the
thermal behavior of anode
-5
-2
2wt % LiBOB
No additive
-3
2wt % VEC
-2
-1
0
60
110
Heat rate, Exoup (W/g)
Heat rate, Exoup (W/g)
-4
160
2wt % LiBOB
2wt % VEC
-1
No additive
2 wt % VC
0
210
260
Temperature (oC)
60
CESE
2 wt % VC
80
100
310
360
120
140
160
o
Temperature ( C)
November 13, 2009
180
200
Electrolyte modification: FR additives
H3CO
N
H3CO
P
N
N
P
Without HMTP
With 1.5 wt% of HMTP
216 oC
3.2
OCH3
OCH3
Hexa-methoxy-cyclo-tri-phosphazene
(HMTP)
Cathode
4
P
2.4
1.6
241 oC
0.8
Heat Flow, W/g EXO UP
Heat Flow, W/g EXO UP
H3CO
OCH3
Anode
2
Without HMTP
With 1.5 wt% of HMTP
1.5
243 oC
1
0.5
120 oC
0
50
100
150
200
Temperature,
CESE
250
300
235 oC
0
50
oC
November 13, 2009
100
131 oC
150
200
250
Temperature, oC
300
Core-Shell approach to improve thermal safety
ARC
50oC delay
1000
225
Core Shell cell
Core cell
200
100
Self Heat Rate ( C/min)
125
100
Thermal Runaway Start
75
50
25
10
Core
0.1
R eactio n start
(C athode + Electroly te)
Ano de reactio n (Dec omposition of S E I)
0
-25
50
1
0.01
LiNi0.8Co0.1Mn0.1O2
Delayed Reaction
1E-3
100
150
200
250
e
T
m
ra
e
p
tu
re
(o
C
)
50
300
100
200
250
300
350
Temperature ( C)
o
Temperature ( C)
DSC
40
Shell
30
30
Core-Shell
Core-Shell
charged
to 4.3V
charged
to 4.3V
20
Heat Flow (W/g)
Heat Flow (W/g)
150
o
40
10
SOA
cathode SOA cathode
10
Charged to 4.3VCharged to 4.3V
Li[Ni0.5Mn0.5]O2
20
50oC delay
0
0
50
100
50
150
100
200 150
200
250
250300
o
CESE
Core Shell
o
150
o
Self Heat Rate ( C/min)
175
Core
Thermal runaw ay delayed by
~50o C delay
November 13, 2009
Temperature ( C)
Temperature (oC)
300
350 350
Acknowledgments
 Dr. Evren Gunen
 Dr. H. Bang
 Dr. Hui Yang
 Dr. C. Lee
 Dr. D. Dess (ANL)
 Dr. K. Amine (ANL)
 Prof. Y. K. Sun (Hanyang U., S.
Korea
CESE
November 13, 2009