Designing a reference electrode – An approach to fabricate laser perforated reference electrodes for lithium-ion batteries

Reference electrodes (REs) are powerful tools to analyze electrochemical phenomena within lithium ion batteries. However, their design and material choice are under debate. Recently, lithium titanate oxide (LTO, Li4Ti5O12) and lithium iron oxide (LFP, LiFePO4) have been dip-coated onto wide-meshed metal nets to reduce the blocking effect. Still, this process is elaborate and not common in electrode manufacturing. In this study, we show a post-processing method to fabricate user-defined REs based on LFP via an ultrashort pulse laser. The REs are designed in such a way that the blocking of the Li+ ion pathways should be as small as possible. Testing these special REs in NMC811/graphite full pouch cells revealed slim to no influence on the cell capacity while delivering reproducible voltages at low to moderate C-rates. Moreover, cell thickness change measurements at the RE site showed no influence on the cell expansion during cycling. Finally, we compare the measured graphite profiles with the ones measured by a conventional Li RE and confirm the comparability of both systems.