Development of high-performance Na/NiCl sub 2 cell Page: 1 of 10
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DEVELOPMENT OF HIGH-PERFORMANCE Na/NiCI2CELL
L. Redey. J. Prakash, D. R. Vlssers, and K. M. Myles
Electrochemical Technology Program
Chemical Technology Division
Argonne National Laboratory
9700 S. Cass Ave., Argonne, IL 60439
The performance of the Ni/NiClz positive electrode for the
Na/NiCI, battery has been significantly improved by lowering the
impedance and increasing the usable capacity through the use of
chemical additives and a tailored electrode morphology. The
improved electrode has excellent performance even below 200 C
and can be recharged within one hour. The performance of this
new electrode was measured by a conventional galvanostatic
method and by a newly developed 'powerdynamic method.
These measurements were used to project the performance of 40-
to 60-kWh batteries built with this new electrode combined with
the already highly developed sodium/p"-aiumina negative
electrode. These calculated results yielded a specific; poweir of
150-400 W/kg and a specific energy of 1 10-200 Wh/kg for
batteries with single-tube and bipolar cell designs. This high
performance, along with the high cel, voltage, mid-tempejaure
operation, fast recharge capability, and fhor^'rc^dh g ®
mode of the electtode couple, makes the Na/NiCI2 battery
attractive for electric vehicle applications.
The cell diagram of the Na/NiCI2 cell is
- Ni/Na/^-alumina/NalAICIJ, NaCI/NiCI^Ni + f >)
Sodium and Na[AlCl4] are molten at the operational temperature
(170 to 400°C) of the cell. Na[AICI4] is added to the porous
Ni/NiCI2 electrode to transport Na+ ions from sudace °f'
alumina electrolyte to the reaction sites at the interior of the
positive electrode. The cell reaction is
2Na + NiCI2 = 2NaCI + Ni (2)
These cells are under intensive development In EnglancI and
circuit within the cell. The specific power and ener y o he
oresent battery construction, however, are modest due to the
performance-limiting positive electrode. To J'*
problem, we sought to improve the performance of this electrode
and to better understand its charge and discharge processes.
Our earlier potentiometric, coulometric, cy°*i°'1
voltammetric investigations on nonporous Ni electrodes [1,2]
suggested that a low-conductivity NiCI2 layer formed on the.
electrode during charge. The increasingly higher resistance of the
charge product stopped the further thickening of the layer and
thereby limited the charge uptake and, consequently, he
available capacity in the subsequent discharge. We termedI this
available capacity "area-capacity limit" (ACL). Depending on the
conditions e. g., temperature, the ACL is 0.4-0.8 C/cm2 of the
true surface area of the nonporous nickel electrode. During
riiftRhnroe. on the other hand, the NaCI formation (Eq. 2).
----- ~ . .____hinhar imnpfianr.fi. nmiiBQ uywei.
These earlier studies also suggested that a porous electrode with
a specially tailored morphology would improve performance by _
providing high surface area and sufficient pore cavities to support
effective mass transport. Also, we found Indications with these
experiments that chemical additives would Improve the properties
of the electrochemicaily forming NiCl2 layer.
Based on the earlier work, we initiated systematic research to
improve the Ni/NiCI2 electrode. As a result, a breakthrough was
achieved in 1991. The usable capacity was increased by five
times and the area-specific impedance of the Ni/NiCI2 electrode
was reduced to one-third that of a baseline electrode . Figure 1
shows the area-specific impedance (AS]1S,), measurecI by-an
interrupted galvanostatic method, as a function of discharged
capacity per unit volume for several porous Ni/NiCI2 electrodes.
The baseline electrode represents our electrode fabncated without
additives using an earlier sintering process characteristic for mid-
1990. The usable capacity defined in this figure is the discharge
capacity when the area-specific impedance (ASI,5s) reaches 4
ohm cm2 or the cell voltage drops to 1.9 V. The termination points
of the curves at progressively higher utilized capacities indicate
increased available energy density (Wh/cm3), and the lowered
area-specific impedance of the Nl/NiCI2 electrod®'
indicates higher power capability. The^ ASI o the Ni/N C a
electrode was calculated by subtracting the ASI of the NaJp -
alumina electrode, which was measured in separate expenments,
from the cell value.
Use of a single additive significantly improved electrode
performance, as shown by the higher available specific energy
and the much lower area-specific Impedance in Fig. 1. The
morphology of the sintered Ni/NICI2 electrode was modified by
using a poreformer during fabrication to attain controlled P°f®'®ize
distribution. This modified morphology along with an additive
further improved performance. Recently, we found that a
combination of the additives in the modified morphology electrode
has a significant synergistic effect, producing even more energy
per unit volume and even lower area-specific impedance. The
chemical additives produce high nickel utilization and low
electrode impedance, probably due to doping effects. By an
optimal combination of additives, we were able to increase ne
utilization of the nickel matrix from 15% to about 45%.
We have studied the effects of pore-size distribution on
electrode performance by measuring capacities of mode
electrodes of various porosities (nonporous Ni, Nt felt, Ni powder
sintered with and without poreformer) under identical conditions.
From the results, we determined the optimum pore-size
distribution of the nickel electrode. Results also indicated that
capacity density (mAh/cm3) improved with increased BET surface
area [41. These measurements provided firm theoretical basis for
the improvement of the modified-morphology Ni/NiCI2 electrodes
shown in Fig. 1.
Performance Measurements of Research Ceils
For exact measurements of the energy density and area-
Hocinned and ooerated small Na/NiCU
IfHscharcfe^o^ the° otheMhand, the NaCI formation (Eq. 2). and operated small Na/NiC.?
accompanied by increasingly higher impedance, nmuea powm. rgSearch cens 0f about 0-6jT .|Ah capacity. The researen ceu
DKTBJBUTION OF THIS BQCilMfUT .IS jJNll!¥HT£D^ |*
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Redey, L.: Prakash, J.; Vissers, D.R. & Myles, K.M. Development of high-performance Na/NiCl sub 2 cell, article, January 1, 1992; Illinois. (digital.library.unt.edu/ark:/67531/metadc1070707/m1/1/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.