2004 Volume 72 Issue 2 Pages 117-122
Tokyo Electric Power Company, Inc. (TEPCO) and NGK Insulators, LTD (NGK) have developed Sodium Sulfur (NAS) Battery. Outstanding feature of the battery is high durability of the charge and discharge cycles. This report presents the electrical performance change of NAS Battery and internal inspection. It is said that degradation of NAS battery is closely related to the protection layer on sulfur case. In this reports it is revealed that the degradation is caused by the two kinds of resistance rise. One of them is ohmic resistance rise which leads to the charge-discharge efficiency loss. We has reached conclusion that resistance rise is caused by the corrosion products formed on the sulfur case. The other is polarized resistance rise which leads to capacity loss. This polarized resistance rise, seen in only 2-phase-region during charge, is caused by corrosion products solved into sulfur electrode.