SENSOR FOR DETECTING DEFORMATION OF SEALED SECONDARY BATTERY, SEALED SECONDARY BATTERY, AND METHOD FOR DETECTING DEFORMATION OF SEALED SECONDARY BATTERY

A sensor for detecting a deformation of a sealed secondary battery, comprises a polymer matrix layer and a detection unit, wherein the polymer matrix layer comprises a filler dispersed in the layer and giving a change to an external field in accordance with a deformation of the polymer matrix layer, and the detection unit detects the change of the external field; and the polymer matrix layer has a glass transition temperature (Tg) of -30°C or lower. It is preferred that the polymer matrix layer comprises a magnetic filler as the filler, and the detection unit detects a change of a magnetic field as the external field.