Operando Dissolution of RF Magnetron-Sputtered Thin-Film LiCoO2 Cathodes during Galvanostatic Cycling: In Situ Evaluation of Dissolution and Performance Data

The dissolution of cathode active material (CAM) results in performance degradation and safety issues and is, thus, a major issue regarding battery aging. While dissolution data have been reported for different cathode compositions after extended cycling, information on potential-dependent transition metal (TM) dissolution for individual charge–discharge cycles is still scarce. In this work, we tackle this subject using an electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry (EFC-ICP-MS) setup presented in our previous publications. By employing radio frequency magnetron-sputtered thin-film LiCoO2 (tf-LCO) cathodes, we obtain time- and potential-resolved dissolution profiles for an accelerated cycling protocol. These results are compared to operando dissolution data of commercial composite cathode tapes (c-LCO). We find uniform dissolution throughout three cycles for tf-LCO, but relative dissolution is higher compared to that of the composite samples by a factor of about 50. During the second cycle, the dissolution characteristics of the c-LCO change and strongly resemble the tf-LCO pattern henceforth. Both types of LCO cathodes experience the largest dissolution during the second cycle, which can be correlated to the irreversible phase transitions of the materials during cycling. Our work represents the first direct investigation of mechanistic changes in transition metal dissolution from lithium-ion battery cathodes and highlights the importance of morphology and cathodic interface properties for dissolution phenomena and battery performance.