For comprehensive monitoring of the battery cell status and early detection of potential thermal runaway issues it is desirable to have real time monitoring of the temperature of each single battery cell. So far, this has not been practical in commercial use due to high cost and high installation effort in temperature sensor integration. Also, the overall reliability of the monitoring system is challenged when using a high number of individual sensors and electrical signal connections. Some attempts have been made to address these challenges by introducing printed electronics/flexible circuit boards to carry sensors and interconnections or by using optical fibres for distributed measurement. Nevertheless, these technologies face challenges with regard to installation, thermal contact and self-test capability.

We report for the first time a novel approach introducing the well-known thermocouple principle for temperature measurement to the process step of electrical contacting the power terminals of each battery cell. The principle is demonstrated for cylindrical cells but can be applied to other cell types. All cells are geometrically arranged in parallel with the positive terminal facing upwards. Thereby, electrical contacting can be localized at the top side of the setup while all the rest is available e.g. for cooling arrangements. The single side cell connection is provided by thick copper tracks on a PCB. Above each cell, copper tongues are present in a PCB through hole which are laser welded to the cell terminals (Fig. 1, 2). The PCB has a thick copper layer for power distribution to charge and discharge the cells and thin copper layers for BMS, sensors and integration of electronics. A CuNi layer (Fig. 1) was added with a respective CuNi tongue to be laser welded to the terminal simultaneously with the thick copper tongue (as the power cell connection). With this step, we form a type T thermocouple between copper and CuNi with self test capability: If the thick copper detaches from the cell, the BMS can detect it. If the CuNi detaches, the thermocouple readout will detect it. I.e. no failure mode due to detachment exists which will not be detected. This addresses a major drawback of other solutions where a temperature sensor detachment from the cell is not detected and the sensor system reports normal temperature although the cell temperature is already rising. Moreover, this single cell temperature monitoring approach does not require any sensor installation or cabling. Therefore, it is cost efficient and very robust.

To simplify PCB processing, the concept was extended to an approach without the CuNi tongue by creating the thermocouple inside the PCB at a via (interconnection) between copper and CuNi (Fig. 3). The via is very close to the cell location to allow for still accurate cell temperature monitoring. The paper will show results of sensor characterization and describe the experience in integration towards a battery module (Fig. 4). The module contains all the electronics for individual temperature readout. Electronics are placed on the same PCB used for power distribution using a galvanically decoupled interface. Differential measurement minimizes the influence of compensation currents.