Disclosed herein is an additive for improvement in safety of an electrochemical device, including an inner core and an outer coating layer, wherein the inner core is formed using a volume-expandable material fused at more than a predetermined temperature while the outer coating layer is formed using a conductive material with higher conductivity than that of the inner core and covers an outer face of the inner core. The disclosed additive rapidly increases resistance of the electrochemical device before ignition/explosion of the device caused by temperature rise, thereby effectively preventing ignition/explosion of the electrochemical device without deterioration in performance of the electrochemical device.