Investigation on

Microstructure and

Conductivity

of ZEBRA Battery Cathode

Tannaz Javadi

Dr. Anthony PetricDr. Gianluigi Botton

MTLS 702

1

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

Contents:

2

Anode (-): Na metal

Cathode (+): Transition metal chloride

+ Excess metal

ElectrolyteSolid electrolyte: β“-Alumina (≥ 0.2 Ω -1cm-1 at 260 ˚C)

Liquid electrolyte: NaAlCl4 (0.6 Ω -1cm-1 at 250 ˚C)

J.L . Sudworth, J. Pow. Sour., 100 (2001)

ZEBRA battery 1978 ZEolite Battery for Research in Africa

FeCl2 NiCl2

Ni- Cu composite Current Collector

2.58 V @ 300 ˚C2.35 V @ 250 ˚C

(200- 300 ˚C) (200- 400 ˚C)

3

Na

NaCl+Ni

NiCl2

NaAlCl4

Liquid electrolyte

+ve Current Collector

Charged area

Discharged area

Reaction front

-ve Cell case

Solid ceramic electrolyte

Na ionsrout

e

Introduction:

Na = Na+ + e- Negative electrode

NiCl2 + 2Na+ + 2 e- = Ni + 2NaCl Positive electrode

2NaCl + Ni NiCl2 + 2Na E = 2.58 V @ 300 ˚C

Charge

Discharge

Anhydrous NiCl2 and Na Loading in discharged state

Micron size

4

Cycling reactions:

The net reaction:

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.

1

1- The cathode-β” alumina interface 2- The cross section of the cathode from β”- alumina to current collector

Vacuum Distillation: Heated up to 450˚C, under vacuum for 4 h.

2345678910

11

12

13

1415

2

β“-Al2O3Current collector

1

5

Experimental materials:

Sample preparation:

10 µ

A: NaCl,B: Ni, C: NaAlCl4

D: NiCl2

E: Na6FeCl82 µ

E

D

A

C

B

1 µ

D

Charged cell

FIB cross section

Discharged cell

6

SEM & FIB Images:

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

7

Thermodynamic modeling

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).

SEM micrographs show that there are Ni particles that are isolated.

In these cases charge transfer may have problems

AB

B

C

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Incentive to improve electrolyte conductivity

Molten salts have relatively low resistivity

Reactive nature of Sodium Chloroaluminate to moisture

Volatile

The U-shaped capillary

High cell constant

Conductance cell design

The U-shaped capillary

The dip-type capillary design

The non-capillary type

High cell constant

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Potentiostat and Frequency Analyzer Nyquist plot

Conductivity measurement of NaAlCl4

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Tungsten wire

Conductivity Cell

Measuring cell constant using different concentration KCl at different temperatures

Concentration(Molarity)

Conductivity (K (Ω-1cm-1))

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)

l = length

A = area

≈ 400 cm-1

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Conductivity Cell Calibration

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Con

duct

ivity

(Ω-1cm

-1)

T (˚C)

Conductivity of pure NaAlCl4 with temperature

Results

0 0.05 0.1 0.15 0.2

-4.99999999999992E-05

7.92822838630025E-19

5.00000000000008E-05

0.000100000000000001

0.000150000000000001

0.000200000000000001

0.000250000000000001

0.000300000000000001 Pure NaAlCl4

I (A

mps

)

E (Volts)

Electronic conductivity of pure NaAlCl4 with temperature

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170 300 4300.35

0.45

0.55

0.65

0.75

0.85

0.95

1.05

Pure NaAlCl45(mol%)NbCl520(mol%)NbCl530(mol%)NbCl540(mol%)NbCl5

ResultsC

ondu

ctiv

ity (Ω

-1cm

-1)

T (˚C)

The conductivity of different percentage of NbCl5 in NaAlCl4

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log

10 (a

ctiv

ity)

Alpha

NbCl5 + <a> Bi

NbCl3 (S)

NbCl4 (S) Nb3Cl8 (S)NbCl4 (S)

Bi (mol)

Thermodynamic modeling; Possible phases at different Mole fraction Bi

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Con

duct

ivity

(Ω-1cm

-1)

T (˚C)

Results Electrical Conductivity with Temp.

140 190 240 290 340 390 440 490 5400.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Pure NaAlCl430%NbCl5+0 mol Bi30%NbCl5+0.2 mol Bi30%NbCl5+0.5 mol Bi

Ele

ctric

al c

ondu

ctiv

ity (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)

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Electrical conductivity (Ω

-1cm-1)

Log

10 (a

ctiv

ity)

(Mole)BiPhases 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

I (A

mps

)

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.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

-0.0001

-0.00005

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.00030.9 mole Bi+ 30 % NbCl5

0.75 mole Bi+30% NbCl5

0.5 mole Bi+30%NbCl5

0.2 mole Bi+30%NbCl5

Pure NaAlCl4

Results Electronic conductivity (300 ˚C)

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Conductivity (Ω-1cm-1)Pure NaAlCl4 0.03830%NbCl5+0.2 mole Bi 0.5330%NbCl5+0.5 mole Bi 0.57230%NbCl5+0.75 mole Bi 0.5730%NbCl5+0.9 mole Bi 0.50

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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Summery

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

Acknowledgement

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Thank you