Hitachi, Ltd.

The Tokyo Electric Power Company, Incorporated

Hisamitu Hatoh

Eiji Takahashi

Sadao Mori

Hiroyuki Kawamoto

Yoshiteru Miyatake

Yasumasa Ishida

Motoi Wada

Disclosed is a method and apparatus which can detect progress of degradation of a sodium-sulfur cell and predict possibility of final breakdown of the cell in a very near future before such a final breakdown of the cell actually occurs. The method and apparatus for diagnosing the presence or absence of an abnormal state in the sodium-sulfur cell, containing a porous electrical conductive material impregnated with molten sulfur or sodium polysulfide as its positive electrode reactant and containing sodium as its negative electrode reactant, comprises observing the operating voltage of the cell during charging and discharging so as to detect occurrence of a minute ripple in the operating voltage, and, when the amplitude of the ripple and the frequency of occurrence of the ripple increases as a result of repeated cycles of charging and discharging, deciding that degradation of the cell has progressed to an extent that final breakdown of the cell will occur in a very near future.

Method and apparatus for diagnosing abnormal state of sodium

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Hitachi, Japan

Hisamitu Hatoh