Theoretical analysis of thermally regenerative bimetallic cells with alkali metal anodes shows a relation between the current drawn and the rate of discharge under open-circuit conditions. The self-discharge rate of the cell is due to the dissolution and ionization of alkali metal atoms in the fused-salt electrolyt

Foster, M. S.

Hesson, J. C.

Shimotake, H.

English

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November 1969	 Brief 69-10631 
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Self-Discharge in Bimetallic Cells Containing

Alkali Metal 
a bime-	 metal atoms and alkali-metal ions and electrons; and 
(ref. 1).
	 (3) the activity coefficient of the dissolved metal 
current	 atoms is consistent with respect to concentration. 
S
A theoretical analysis of self-discharge in 
tallic thermally regenerative cell is reported 
A relation is shown to exist between the 
drawn and the rate of discharge under open-circuit 
conditions. 
Thermally regenerative bimetallic cells, with alkali-
metal anodes, have been considered as a means for 
conversion of thermal to electrical energy. In these 
cells the anode is an alkali metal such as lithium, 
sodium, or potassium; the cathode consists of a 
binary alloy of the alkali metal and a more noble metal 
such as lead, bismuth, or tin. The electrolyte is a 
mixture of molten halides of the alkali metal of the 
anode. The open-circuit potentials of such cells have 
been used for calculation of the thermodynamic prop-
erties of binary alloys. 
It was noted (ref. I) that in sodium-bismuth, bime-
tallic cells having an electrolyte of molten sodium 
fluoride, sodium chloride, and sodium iodide, a non-
faradic or "irreversible" transfer of sodium from 
the anode to the cathode takes place. Since this trans-
fer occurs without producing an electric current in the 
external circuit, it is also called a self-discharge of the 
cell. The self-discharge rate is much too high to be 
explained simply 'by diffusion of dissolved sodium 
atoms through the electrolyte. Moreover, the rate of 
self-discharge decreases with increase in current 
drawn from the cell. 
For the theoretical analysis, an attempt to explain 
the observed self-discharge rate and its anomalous 
behavior with current, it was assumed that (1) the 
self-discharge of the cell is in part due to electronic 
conductivity of the electrolyte, which in turn results 
from and is proportional to dissolved alkali metal; 
(2) an equilibrium exists between dissolved alkali-
The self-discharge rate of a concentration cell is 
considered to be due to the dissolution and ionization 
of alkali-metal atoms in the fused-salt electrolyte. 
On the basis of the outlined assumptions, an expres-
sion was derived that relates the self-discharge rate 
as a function of current. This expression was used 
for construction of graphs showing the effect of cell 
current on the self-discharge rate for a variety of 
conditions. It is demonstrated that the open-circuit 
potential of such a cell is less than that predicted 
from theoretical thermodynamic considerations. 
Reference: 
I. I-lesson, J. C.; Foster, M. S.; Shimotake, H.: Self-
Discharge in Alkali Metal-Containing Bimetallic 
Cells. J. Electrochem. Soc., vol. 115, No. 8, Aug. 
1968, pp. 787-790. 
Notes: 
1. This information may interest researchers in 
electrochemistry or molten-salts chemistry. 
2. Inquiries concerning this information may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10631 
Source: J. C. Hesson, M. S. Foster,
and H. Shimotake
Chemical Engineering Division 
(ARG- 10347) 
-	 (continued overleaf) 
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Patent status: 
Inquiries concerning rights for commercial use of 
this information may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
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Brief 69-10631	 Category 01


Self-discharge in bimetallic cells containing alkali metal

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