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Operando Analysis of High Capacity ELectrodes

Within the SCI program, HZB contributes to Topic 1 “Electrochemical Storage of Energy”. HZB is engaged in the investigation of fundamental aspects of the lithium/sulfur battery. Additional work is being done on the lithium/silicon system. Both systems exhibit high theoretical specific capacity (1675 Ah/kg for sulfur and 4200 Ah/kg for silicon) compared to graphite anodes (372 Ah/kg) and typical lithium-ion cathodes like LiCoO2, LiMn2O4, LiNiMnCoO2, and LiFePO4 with approximately 250 Ah/kg. Their environmental friendliness and abundance qualify these two electrodes as promising candidates for the post-lithium-ion era. However, the strong capacity fading with increasing charge/discharge cycles is the major obstacle that must be overcome for successful broad commercialization. Up to now, the mechanisms behind this degradation that preclude all meaningful technical use are not yet understood and in need of further basic research.

operando-concept - enlarged view

Research-Concept: Operando analysis of silicon anode (left) and sulfur cathodes (right).

Operando studies of electrochemical cells constitute a central part of our work within Topic 1 of the SCI program. The figure above gives an overview of these studies that cover the pertinent length scales ranging from sub-nanometers to millimeters. We believe that these operando studies present a unique contribution to the literature on Li/S cells. Thus, we were able to present the first operando-radiography of a Li/S-cell. Moreover, we published the first operando study of a Li/Si anode using neutron reflectivity. Our set-up is multi-dimensional in all cases, i.e. scattering methods are combined with impedance spectroscopy, UV-vis spectroscopy, temperature and galvanostatic measurements.