Battery System Thermal Event Detection Method and Battery System Using the Same

A battery system includes a battery pack including a plurality of battery cells a pressure sensor located inside the battery pack to measure an internal pressure of the battery pack every sampling cycle; and a battery management system calculating a reference pressure based on an average of internal pressures measured at sampling cycles for a sampling period, calculating a pressure fluctuation amount based on a difference of the internal pressure measured every sampling cycle from the reference pressure, and determining that a thermal event has occurred in the battery pack if the internal pressure measured every sampling cycle increases consecutively at least two times when the pressure fluctuation amount is greater than or equal to a predetermined threshold pressure.