Electrochemical Storage of Energy
HZB contributes within the Helmholtz-program "Storage and cross-linked Infrastructure" (SCI) to Topic 1 “Electrochemical Storage of Energy”. Research done within Topic 1 covers a broad range from fundamental aspects of electrochemical storage materials through manufacturing of components/cells and the engineering of large grids and storage systems. HZB is engaged in the investigation of fundamental aspects of the lithium/sulfur battery. Additional work is done on the system lithium/silicon. Both systems exhibit a high theoretical gravimetric capacity of 1675 Ah/kg and 4200 Ah/kg for sulfur and silicon, respectively, compared to graphite anodes (372 Ah/kg) and typical lithium ion cathodes like LiCoO2, LiMn2O4, LiNiMnCoO2 or LiFePO4 with approximately 250 Ah/kg. Their environmental friendliness and abundance qualify these two electrodes as promising candidate for the post-lithium-ion era. However, the strong capacity fading with increasing charge/discharge cycles is the major obstacle that has to be overcome for a successful broad commercialization. Up to now, the mechanisms behind this degradation that precludes all meaningful technical used are not yet understood and in need of further basic research.
HZB entered the field of electrochemistry in 2014 and aims at a full understanding of the fundamental mechanisms of the system Li/S and Li/Si throughout all pertinent length scales, that is, from the subnanometer range to the millimeter range. The overarching goal is the better understanding of marked capacity fading seen in both systems. Special emphasis is laid on operando studies of electrochemical cells during charging and discharging. Central tools for these studies are SANS and SAXS together with neutron reflectivity and X-ray imaging methods. The HZB has a strong expertise on these methods based on previous work. All operando studies are closely connected to our efforts to synthesize new carbon nanostructures as cathodes for lithium/sulfur cells. Further effort is on novel composite systems that consist of a tailored carbon nanomaterial with a large active surface and inorganic nanometric components that can suppress possible side reactions in lithium/sulfur cells. Also, the simulation of complex molecular transport processes in the multi component electrolyte is an important tool to gain knowledge for further material improvements and mechanistic understanding.