Battery State of Charge and Aging Monitoring via Temperature Differential Analysis for Real World Application

Precision battery monitoring is of upmost importance for safety and cost reasons across a range of applications. However, battery management systems rarely allow for the monitoring of individual cells, since contacts are made to series-connected batteries. Herein, we demonstrate that thermal monitoring of individual cells, achieved using surface-mounted fiber Bragg grating sensors, may illuminate a traditional blind spot for cell and module management. To achieve this, the heat generated from commercial NVPF/HC sodium-ion cells was used to monitor the cell state of charge via the NVPF phase transition. We show that by quantitatively tracking this optically informed metric, it can be used for non-invasive, in-operando cell aging analysis during long-term cycling. With the technique established, we showcase the possibility of spotting a defective cell inside a battery pack configuration, offering the possibility for cell balancing using thermal-based criteria. As a bridge towards real-world applications, sensing data is harvested using a novel and portable optical interrogator with wireless data transmission capabilities, paving the way for cost-effective, reliable, and facile implementation. Finally, our methodology is extended to LFP/Graphite cells, where the heat generated by lithium intercalation in graphite allows for state of charge estimation, demonstrating a universal potential for battery applications.