Transcript Slide 1

Investigation on
Microstructure and Conductivity
of ZEBRA Battery Cathode
Tannaz Javadi
Dr. Anthony Petric
Dr. Gianluigi Botton
MTLS 702
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Contents:
1- Microstructure of the cathode
2- Thermodynamic modeling of ZEBRA cycling
3- Conductivity measurement of the liquid electrolyte with
temperature.
4- Effect of adding additives on liquid electrolyte conductivity
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Introduction:
1978
ZEBRA battery
Anode (-): Na metal
ZEolite Battery for Research in Africa
Ni- Cu composite Current Collector
Solid electrolyte: β“-Alumina (≥ 0.2 Ω -1cm-1 at 260 ˚C)
Electrolyte
Liquid electrolyte: NaAlCl4 (0.6 Ω -1cm-1 at 250 ˚C)
Cathode (+): Transition metal chloride
+ve Current Collector
+ Excess metal
NaAlCl4
Liquid electrolyte
FeCl2
2.35 V @ 250 ˚C
(200- 300 ˚C)
Na
ions
route
NiCl2
NiCl2
2.58 V @ 300 ˚C
(200- 400 ˚C)
J.L . Sudworth, J. Pow. Sour., 100 (2001)
NaCl
+
Ni
Na
Charged
area
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Reaction front
Discharged
area
-ve
Cell
case
Solid ceramic electrolyte
Cycling reactions:
Na = Na+ + e-
Negative electrode
NiCl2 + 2Na+ + 2 e- = Ni + 2NaCl
Positive electrode
The net reaction:
Charge
NiCl2 + 2Na
2NaCl + Ni
Micron size
Discharge
Anhydrous NiCl2 and Na
E = 2.58 V
@ 300 ˚C
Loading in discharged state
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Experimental materials:
Cell 1: charge=48.3 Ah at 325 ˚C, discharge= 40.8 Ah at 295 ˚C.
Cell 3: charge=Similar to Cell1, discharge= 38 Ah at 295 ˚C.
Cell 763: First 12 cycles similar to Cell 3, discharge= 26.2 Ah at 295 ˚C.
Sample preparation:
Vacuum Distillation: Heated up to 450˚C, under vacuum for 4 h.
1- The cathode-β” alumina interface
2- The cross section of the cathode from
β”- alumina to current collector
Current collector
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β“-Al2O3
1
1 1 1 1 1
9 8 7 6 5 4 3 2 1
4 3 2 1 0
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Charged cell
SEM & FIB Images:
Discharged cell
D
1µ
FIB cross section
10 µ
A: NaCl,
B: Ni,
C: NaAlCl4
D: NiCl2
E: Na6FeCl8
D
C
E
A
2µ
B
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Thermodynamic modeling
Room temperature microstructure deviates from real phases
present during operation at high temperature
FactSage database are appropriate
Examination of cell reaction during cycling
for modeling ZEBRA chemistry
Phase changes during cooling
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Thermodynamic modeling
charging
Overcharge (L +NiCl2)
Discharging
Increase in solubility of NiCl2 in molten salt
Ni grain growth
Tannaz Javadi, Anthony Petric, J. Electrochem. Soc., V.158, Issue 6, p. A700-A704, (2011).
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Incentive to improve electrolyte conductivity
SEM micrographs show that there are Ni particles that are isolated.
In these cases charge transfer may have problems
C
A
B
B
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Conductivity measurement of NaAlCl4
Potentiostat and Frequency Analyzer
Nyquist plot
The U-shaped capillary
Conductance cell design
High cell constant
The dip-type capillary design
The non-capillary type
 Molten salts have relatively low resistivity
 Reactive nature of Sodium Chloroaluminate
to moisture
The U-shaped capillary
High cell constant
 Volatile
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Conductivity Cell
Tungsten wire
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Conductivity Cell Calibration
Measuring cell constant using different concentration KCl at different
temperatures
Conductivity (K (Ω-1cm-1))
Concentration
(Molarity)
18 ˚C
25 ˚C
1
0.09783
0.11134
0.1
0.011166
0.012856
0.01
0.0012205
0.0014087
R = Resistance (Ω)
ρ = Resistivity (Ω.cm)
≈ 400 cm-1
l = length
A = area
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Results
Conductivity of pure
NaAlCl4 with temperature
Electronic conductivity of pure
NaAlCl4 with temperature
Pure NaAlCl4
Conductivity (Ω-1cm-1)
0.0003
I (Amps)
0.00025
0.0002
0.00015
0.0001
5E-05
7E-19
0
0.05
0.1
0.15
0.2
-5E-05
T (˚C)
E (Volts)
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Results
The conductivity of different percentage of NbCl5 in NaAlCl4
1.05
Conductivity (Ω-1cm-1)
0.95
0.85
Pure NaAlCl4
0.75
5(mol%)NbCl5
20(mol%)NbCl5
0.65
30(mol%)NbCl5
40(mol%)NbCl5
0.55
0.45
0.35
170
300
430
T (˚C)
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Thermodynamic modeling; Possible phases at
different Mole fraction Bi
NbCl4 (S)
NbCl3 (S)
NbCl4 (S)
Nb3Cl8 (S)
log 10 (activity)
NbCl5 + <a> Bi
Alpha
Bi (mol)
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Results
Electrical Conductivity with Temp.
1.2
Conductivity (Ω-1cm-1)
1.1
1
0.9
0.8
Pure NaAlCl4
0.7
30%NbCl5+0 mol Bi
0.6
30%NbCl5+0.2 mol Bi
30%NbCl5+0.5 mol Bi
0.5
0.4
0.3
140
190
240
290
340
T (˚C)
390
440
490
540
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Electrical
Possible
phases atConductivity
different Mole fraction Bi
NaAlCl4+NbCl5+Bi (300 ˚C)
Log 10 (activity)
Electrical conductivity (Ω-1cm-1)
Electrical conductivity (Ω-1cm-1)
Results
Results
(Mole)Bi
Bi (mole
%)
present
at different concentrations
Bi in
the mixture
at 300 ˚C and their
EffectPhases
of different
concentrations
of Bi added toof
30%
NbCl
5 and NaAlCl4 mixtures at 300 ˚C.
effect on conductivity
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Results
Electronic conductivity (300 ˚C)
Conductivity (Ω-1cm-1)
0.038
0.53
0.572
0.57
0.50
Pure NaAlCl4
30%NbCl5+0.2 mole Bi
30%NbCl5+0.5 mole Bi
30%NbCl5+0.75 mole Bi
30%NbCl5+0.9 mole Bi
0.0003
0.9 mole Bi+ 30 % NbCl5
I (Amps)
0.00025
0.0002
0.75 mole Bi+30% NbCl5
0.00015
0.5 mole Bi+30%NbCl5
0.0001
0.00005
0.2 mole Bi+30%NbCl5
0
0
-0.00005
0.05
0.1
0.15
0.2
Pure NaAlCl4
E (volts)
-0.0001
The I-E curve for different mixtures of NbCl5 + Bi +NaAlCl4.
The scan rate is 1 mV/s and the range of voltage is 0-0.2V vs. Reference.
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Summery
1- Thermodynamic modelling predicts the presence of different phases at operating
temperature and confirmed the SEM results.
2- SEM micrographs from ZEBRA cell cathode reveal the existence of isolated Ni
particles that may not contribute to the cycling reaction as they are all
surrounded by merely ionic conductors.
3- A special conductivity cell with high cell constant was designed to measure the
conductivity of hygroscopic and volatile NaAlCl4.
4- The effect of different additives on conductivity of the liquid electrolyte was
examined by using EIS.
5- Among different additives, 30 % NbCl5 + 0.2 mole Bi shows the best conductivity.
6- The conductivity of the liquid electrolyte approximately doubles between 190 and
490 ˚C.
7- The electronic conductivity of the mixtures were measured by using DC
technique. Results show the presence of electronic conductivity in electrolyte
by adding dopants.
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Acknowledgement
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Dr. Anthony Petric
Dr. Gianluigi Botton
Dr. Gary Purdy
Dr. Gu Xu
CCEM staff
Jim Garrett
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Thank you
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