1. Microstructure and Conductivity of ZEBRA Battery Cathode
Investigation on
Microstructure and Conductivity
of ZEBRA Battery Cathode
Tannaz Javadi
Dr. Anthony Petric
Dr. Gianluigi Botton
MTLS 702

2. 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

3. Solid ceramic electrolyte
Introduction:
1978
ZEBRA battery
ZEolite Battery for Research in Africa
Anode (-): Na metal
Ni- Cu composite Current Collector
Solid electrolyte: β“-Alumina (≥ 0.2 Ω -1cm-1 at 260 ˚C)
Liquid electrolyte: NaAlCl4 (0.6 Ω -1cm-1 at 250 ˚C)
Electrolyte
Cathode (+): Transition metal chloride
+ Excess metal Na
NaCl + Ni
NiCl2
NaAlCl4
Liquid electrolyte
+ve Current Collector
Charged
area
Discharged
Reaction front
-ve
Cell
case
Solid ceramic electrolyte
ions
route
FeCl2
NiCl2 ˚C ˚C
( ˚C)
( ˚C)
J.L . Sudworth, J. Pow. Sour., 100 (2001)

4. Cycling reactions: The net reaction: Na = Na+ + e- Negative electrode
NiCl2 + 2Na+ + 2 e- = Ni + 2NaCl Positive electrode
The net reaction:
2NaCl + Ni
NiCl2 + 2Na E = 2.58 V
@ 300 ˚C
Charge
Discharge
Micron size
Anhydrous NiCl2 and Na
Loading in discharged state

5. 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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
β“-Al2O3
Current collector 1

6. SEM & FIB Images: Charged cell Discharged cell FIB cross section
1 µ D
10 µ
Discharged cell
2 µ E D A C B
FIB cross section
A: NaCl,
B: Ni,
C: NaAlCl4
D: NiCl2
E: Na6FeCl8

7. Thermodynamic modeling
Room temperature microstructure deviates from real phases
present during operation at high temperature
FactSage database are appropriate
for modeling ZEBRA chemistry
Examination of cell reaction during cycling
Phase changes during cooling

8. Thermodynamic modeling
charging
Discharging
Overcharge (L +NiCl2)
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).

9. Incentive to improve electrolyte conductivity
SEM micrographs show that there are Ni particles that are isolated.
In these cases charge transfer may have problems A B C

10. Conductivity measurement of NaAlCl4
Potentiostat and Frequency Analyzer
Nyquist plot
The U-shaped capillary
The dip-type capillary design
The non-capillary type
High cell constant
Conductance cell design
Molten salts have relatively low resistivity
Reactive nature of Sodium Chloroaluminate
to moisture
Volatile
The U-shaped capillary
High cell constant

11. Conductivity Cell
Tungsten wire

12. Conductivity (K (Ω-1cm-1))
Conductivity Cell Calibration
Measuring cell constant using different concentration KCl at different temperatures
Concentration
(Molarity)
Conductivity (K (Ω-1cm-1))
18 ˚C
25 ˚C 1
0.1
0.01
R = Resistance (Ω)
ρ = Resistivity (Ω.cm)
l = length
A = area
≈ 400 cm-1

13. Results Conductivity of pure Electronic conductivity of pure
NaAlCl4 with temperature
I (Amps)
E (Volts)
Electronic conductivity of pure
NaAlCl4 with temperature
Conductivity (Ω-1cm-1)
T (˚C)

14. Results The conductivity of different percentage of NbCl5 in NaAlCl4
Conductivity (Ω-1cm-1)
T (˚C)

15. Thermodynamic modeling; Possible phases at different Mole fraction Bi
NbCl3 (S)
NbCl4 (S)
NbCl4 (S)
Nb3Cl8 (S)
log 10 (activity)
Alpha
NbCl5 + <a> Bi
Bi (mol)

16. Results Electrical Conductivity with Temp.
Conductivity (Ω-1cm-1)
T (˚C)

17. Results Electrical Conductivity NaAlCl4+NbCl5+Bi (300 ˚C)
Electrical conductivity (Ω-1cm-1)
Bi (mole %)
Effect of different concentrations of Bi added to 30% NbCl5 and NaAlCl4 mixtures at 300 ˚C.
Results Electrical Conductivity
NaAlCl4+NbCl5+Bi (300 ˚C)
Electrical conductivity (Ω-1cm-1)
Log 10 (activity)
(Mole)Bi
Phases present at different concentrations of Bi in the mixture at 300 ˚C and their effect on conductivity
Results Possible phases at different Mole fraction Bi

18. The I-E curve for different mixtures of NbCl5 + Bi +NaAlCl4.
Results Electronic conductivity (300 ˚C)
Conductivity (Ω-1cm-1)
Pure NaAlCl4
0.038
30%NbCl5+0.2 mole Bi
0.53
30%NbCl5+0.5 mole Bi
0.572
30%NbCl mole Bi
0.57
30%NbCl5+0.9 mole Bi
0.50
I (Amps)
E (volts)
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.

19. 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 % NbCl 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.

20. Dr. Anthony Petric Dr. Gianluigi Botton Dr. Gary Purdy Dr. Gu Xu
Acknowledgement
Dr. Anthony Petric
Dr. Gianluigi Botton
Dr. Gary Purdy
Dr. Gu Xu
CCEM staff
Jim Garrett

21. Thank you