Operando Monitoring of Electrode Temperatures During Overcharge‐Caused Thermal Runaway

Lithium‐ion batteries’ (LIBs) failure due to abusive cycling conditions can result in thermal runaway, which calls for reliable real‐time battery thermal safety monitoring. Herein, an effective method for LIB thermal runaway detection using a resistant temperature detector (RTD) is compared with a conventional battery surface temperature measurement. A direct electrode temperature measurement technique based on additive manufacturing‐enabled application of miniature RTDs for measurement of internal temperature within large‐capacity Li‐ion pouch cells is used. The miniature RTDs are embedded in a customized electrochemically inactive polymeric substrate for real‐time thermal safety monitoring during overcharge abuse. Electrode temperature profiles under different conditions of overcharge (at 1 and 5 C rate, charged until battery explosion) are analyzed and mechanisms of heat generation in LIBs during overcharge‐induced thermal runaway are investigated. The internal RTDs detect the onset temperature of the solid−electrolyte interface decomposition ≈10 s earlier than the sensors attached to the battery surface. A maximum temperature gradient of ≈200 °C is observed between the electrode and the battery surface during overcharge‐induced thermal runaway. The internal RTDs are shown as a possible guide for sensor placement location to capture the maximum temperature within the LIBs during abuse events. Herein, internal temperature sensors to directly monitor the electrode temperature of large‐capacity Li‐ion pouch cells during extreme overcharge conditions to observe mechanisms of heat generation, leading to thermal runaway, are utilized. Results are compared with external temperature sensors to determine the temperature gradient during overcharge and the difference in indication time between internal and external sensors is observed.