Internal temperature evolution of lithium-ion battery over long-term cycling via advanced fiber sensing

Accurate internal temperature monitoring for lithium-ion batteries over the whole lifespan is critical to determine their performance and develop the management techniques. Facing the challenging task of unlocking the internal temperature by a non-destructive technique, a commercial miniature measurement device involving optical sensors is developed, in which the optical sensor is implanted inside the battery with an integrated functional electrode design. Long-term cycling tests are conducted on pouch cells showing capacity retention of 74.94 % after 1300 cycles at 1C and 71.14 % after 1300 cycles at 2C. The sensing technology does not affect the electrochemical performance of the battery, and further evidence is supported by the post-mortem analysis. A prediction formulation of the temperature rise rate during the discharge process throughout the life cycle is established by investigating the temperature evolution over the whole lifespan of the cell, and the error of the fitting result is less than 5 %. Furthermore, the disappearance of the temperature plateau is developed as an evaluation indicator to monitor whether the battery capacity fade is close to 80 %, and the suitable criterion achieves an estimation error of less than 1 %. Moreover, for the cell of NCM-M-2C, after 1300 cycles, the temperature rise rate increased from 0.22 °C/min (beginning of life) to 0.55 °C/min (end of life) under 2C constant current discharging condition. This study opens new avenues to develop advanced battery management and the design of safer energy-dense batteries through operando sensing.