In Situ Detecting Lithium-Ion Batteries Thermal Runaway with Resistance Temperature Detector

Advanced next-generation lithium-ion batteries (LIBs) can only be realized when the thermal safety-related incidents, which have been the roadblocks for development, are mitigated. A variety of advanced works have been proposed for safety enhancement viz., isolating shutdown separators, protective electrode coatings, electrolyte additives. However, they have been stalled from further developments on account of their narrow range in working voltage window, stability, performance, and response time. Also, to date in situ safety devices are known to drastically affect LIBs' performance. Novel temperature measurement schemes have been developed to help battery management systems (BMS) for improved prediction such as Thermocouples, Thermistors, Fiber Bragg-grating (FBG) sensors, etc. but each has its limitation. Hence, this points towards developing an effective temperature management system that is capable of quick detections, compact, cost-effective, and light-weighted. Here, we are reporting in operando thermal runaway detection for LIBs, from beneath the anode current collector, using an internal resistance temperature detector (RTD). Sensing temperature fluctuations from the anode is more critical compared to the cathode is that it has a solid electrolyte interface (SEI) layer, which is comprised of reduced electrolytic compounds like ROCO₂Li, (CH₂OCO₂Li)₂ and ROLi and has lithium stored in graphitic interlayers. During thermal runaway events, decomposition of these compounds and reactions of the charged anode with electrolyte leads to the generation of an enormous amount of heat, which can induce fire, smoke, or explosion. Hence, sensing the anode becomes critical and gives direct access to this heat.

Here, we studied three such thermal runway events, viz, external short circuit (ESC), overcharging, and overheat using multiple module calorimetry (MMC) to elucidate the thermal detection capabilities and presence of RTD inside the LIB. During ESC and overcharge tests, temperatures of around 36°C and 48°C were recorded using internal RTDs, respectively. These temperatures were about 9°C and 20°C more than the external RTDs. An interesting statistic about the internal RTD was its detection ability, which for 90% temperature rise was about 14 times faster than compared to the external RTD. RTD embedded mesocarbon microbeads (MCMB) anode half-cell was cycled at 0.25C rate giving a stable average capacity of 238 mAh g^-1 over 200 cycles with voltage profile congruent to those reported in the literature. Modeling simulated tests elucidated the prevalence of different regions during thermal runaway events initialed by ESC and overcharge. Additionally, Multimode Calorimetry (MMC) for LIB with embedded internal RTD produced more endothermic peaks beyond 150°C and overall heat generated was 1.75 kJ g^-1, which is significantly lower than conventional LIB. RTD assembly has another role of being a passive safety device while placed inside the LIB. Using thermal signatures from internal RTD, future BMS can provide a conducive environment for the LIBs, which would deliver power for high energy density applications such as in the grid-storage and EVs industries.