Designed interfaces for electrochemical energy storage

We combine state-of-the-art surface and interface characterization techniques with materials design to develop next generation negative electrode materials for rechargeable batteries.
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Figure 1: Schematic representation of an SEI depth profile using synchrotron photoelectron spectroscopy.


Interfaces and Interphases play a key role in rechargeable batteries such as Li-ion batteries because they determine important factors such as stability, reversibility and safety. One particularly important interphase is the solid electrolyte interphase (SEI). The SEI forms during battery operation on the negative electrode surface as a result of electrolyte decomposition. This is connected to irreversible capacity losses, as the charges consumed in the electrolyte decomposition cannot be recovered. However, in the ideal case, the SEI passivates the electrode’s surface and thus hinders continuous electrolyte decomposition.






Tailored electrode protection layers


The focus of our research activities is to understand the SEI formation in such detail that we will be able to design these important interfaces to improve battery performance and to develop the next generation of safe and stable high-performance battery systems. Since the SEI itself is only a few tens of nanometers in thickness, we apply state-of-the art surface and interface characterization techniques to follow its formation and evolution in a battery combined with electrochemical characterization.


At the IAM-ESS, we use x-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (TOF-SIMS) and scanning electron microscopy (SEM) (Surface & Interface analytics). In addition, we work with the development of novel in-situ characterization techniques such as ambient pressure photoelectron spectroscopy (AP-PES).


Project InSEIde


Within the project “InSEIde”, we apply this approach to Silicon/Carbon (Si/C) composites. This material is likely to replace graphite, which is currently used as anode material, in next generation lithium ion batteries. Transitioning to Si/C electrodes boosts the battery performance as silicon is capable of storing about ten times the charge of graphite.


This vast energy storage does however bring significant challenges, mainly in the electrode/electrolyte interface. Large volume changes in the electrode material causes severe strain on the SEI and the SEI is often seen to brake during extended cycling. This exposes fresh surface leading to a continuous SEI formation to repair the film, ultimately causing capacity losses. In order to unlock the true potential of these promising Si/C electrodes, we need to develop a stable and flexible SEI layer for this material class.



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