Integrated Sensor Printed on the Separator Enabling the Detection of Dissolved Manganese Ions in Battery Cell

Conventional monitoring of Li-ion battery cell performance is carried out by combining empirical measurement of the extrinsic parameters with multipart modeling and approximation algorithms. A step forward would be enabling more reliable built-in sensing systems that allow collecting direct information, such as a degree of constituting materials degradation. Transition metal dissolution is one of the most severe degradation processes affecting the performance of the whole battery cell. It can be accelerated through different mechanisms, and its monitoring has been a topic of several studies in recent decades. In this work, we establish an approach for unambiguous detection of dissolved manganese ions via the built-in electrochemical sensor with scavenger moieties. We demonstrate that manganese ion-imprinted polymer (Mn(II)-IIP) deposited between two electrodes printed directly on the separator can be used as a sensing layer. The resistance of this sensing layer changes due to the coordination of the ion-imprinted polymer with dissolved manganese ions and this is then precisely monitored by the electrochemical impedance spectroscopy in the mid-frequency range. Both the electrodes and sensing layer remain stable within the voltage range of battery cycling over a longer application time. The sensor performance was validated in the single-layer pouch cell using Li||LiMn2O4 chemistry. The use of printing technology permits large-scale commercialization; sensors printed on the separator do not significantly alter the current production technology and, most importantly, have a negligible impact on the cell energy density. The approach is universal and can eventually be extended to the detection of other degradation products in the electrolyte.