Battery Cell Temperature Sensing Towards Smart Sodium-Ion Cells for Energy Storage Applications

Battery cell instrumentation (e.g., temperature, voltage and current sensing) is vital to understand performance and to develop/contrast different cell designs and chemistries. Sodiumion batteries (NIBs) are emerging as an alternative solution to lithium-ion (LIB) technology, particularly in the field of grid energy storage. The relative abundancy of sodium (Na) and superior charge/discharge capability, fuel the development effort to match the desirable energy density properties of LIBs. Internal temperature sensing is of particular value during cell development, offering insights into hot spots and manufacturing defects, in-advance of detection via voltage or surface temperature measurement. We developed novel thermistor arrays (7x miniature sensors) inserted into the core of a 21700 format LIB via flexible PCBs. These arrays were protected using a covering tube, and successfully provided temperature measurements throughout an ageing experiment consisting of 100 cycles (1C charge, 0.3C discharge). For the first time, we report on our performance tests prior to this ageing study (capacity, internal resistance) to highlight the instrumented cells show comparable degradation $(\sim 5\ \%)$ to an unmodified cell. We extend this study by verifying that our scalable low-cost solution to sensor protection can be migrated to NIBs. The resilience of the protected PCBs to electrolyte was tested via a longer-term test (preliminary results from a 90-day study are reported here) submerged within the solution. The findings offer a promising outlook to lower-cost cell instrumentation and will provide a tool to optimize these novel cell chemistries.