PURPOSE: To improve corrosion resistance to sodium polysulfide by forming a high concentration chromium-aluminum-iron alloy layer on the surface of a battery cell for sodium-sulfur battery.

CONSTITUTION: A chromium calorizing treating agent is obtained by adding cerium or a mixture of cerium with lanthanum as an accelerator for accelerating forming the chromium-aluminum-iron layer on the surface of a battery cell base material into a mixed agent for chromium calorizing working composed of 30-60% powdery chromium, 5-10% powdery aluminum, 0.5-2.0% powdery ammonium chloride and 20-50% powdery alumina. The battery cell base material composed of steel or iron low in carbon content is chromium calorized by using the treating agent. Having strong attractive force to metals, cerium atom or lanthanum atom is adsorbed on the surface of the battery cell base material and simultaneously the adsorption of chromium atom and aluminum atom on the surface of the battery cell base material is accelerated.