This work demonstrates the development and evaluation of sensing technology for monitoring the distributed in-situ in-operando temperature of lithium-ion cells. The influence of the sensing element on the electrochemical system was evaluated using EIS, CT scanning and cell cycling characterisation and was proven to be negligible. Furthermore, the thermal sensors were proven to be resistant to the strain imposed during the cell instrumentation procedure and the harsh chemical environment inside the Li-ion cells. The sensing methodologies and modification techniques developed in this work can be applied to large scale battery modules and pack systems and integrated within the cell manufacturing process. This work identified a clear and significant difference between the cell’s can and core temperatures, as well as axial temperature gradient. The findings of this study are of significance to the performance and safety limits of energy storage systems. This research indicates the clear need for reliable sensing systems that enable accurate in-situ in-operando monitoring of lithium-ion energy storage systems.