Abstract
<jats:p>Electrochemical direct Li extraction (eDLE) enables the utilization of unconventional new Li sources such as geothermal brines. Methods based on ion intercalation, which operate similarly to Liion batteries, are particularly promising. To rationally design respective materials and processes, a phenomenological and mechanistic understanding of the physics and chemistry underlying (de-)intercalation and degradation is needed. Ideally, this knowledge is quantitative, bridges the atomic and mesoscopic scales, and can be interpreted in the context of material and device performance under various operating conditions. Given the complexity of electrochemical Li-capturing system (ELiCS) reactors, this task is challenging, and innovative approaches using advanced operando methods are necessary. Towards this end, we devised an operando high-energy X-ray diffraction (HEXRD) microscopy study of spinel manganese oxide Li extraction electrodes under realistic conditions. For this purpose, we designed a realistic flow-by reactor, integrated into a quasi-high-throughput system, allowing us to investigate the atomic scale structural evolution across the electrodes during operation. Our results suggest a peculiar phase evolution exhibiting a three-phase coexistence of variously lithiated phases and a complex combination of solid solution reactions and bi-/tri-phasic phase transitions with significant heterogeneity across the electrode. Intriguingly, we observe a markedly asymmetric behavior in the phase evolution during lithiation and delithiation, indicating significant differences in intercalation and deintercalation mechanism. We rationalise our results, interpret their implications for ELiCS performance, and discuss how they inform ELiCS process design.</jats:p>