Elucidating the Structure and Function of the Electrode-Electrolyte Interface by New Solid State NMR Approaches

The development of high-energy, long-lasting energy storage systems based on rechargeable batteries relies on our ability to control charge storage and degradation processes in the bulk of the materials and at their interfaces. NMR spectroscopy is exceptionally suited to follow the electrochemical and chemical processes in the bulk of the electrodes and electrolyte, providing atomic scale structural insight into the charge storage mechanisms and ion transport properties. However, interfacial properties, such as the processes governing charge transport between the electrode and the electrolyte, are much harder to study. These processes typically involve thin, heterogeneous and disordered layers that are formed chemically/electrochemically in the battery cell or artificially through coating the electrode material. While NMR is in principle an excellent approach for probing disordered phases, its low sensitivity presents an enormous challenge in the detection of interfacial processes.<br/>I will describe recent approaches to overcome this limitation by the use of Dynamic Nuclear Polarization (DNP). In DNP, the large electron spin polarization is used to boost the sensitivity of NMR spectroscopy by orders of magnitude. I will show how we can use this approach, using exogenous and endogenous sources of polarization, to detect buried solid interphases (such as the SEI), electrode coatings as well as the electrode’s bulk, with unprecedented sensitivity. Furthermore, I will present new approaches to probe ion transport properties of metal electrodes interfaces in solid and liquid electrolytes. These allow us to get insight into the functional role of interfaces, which along with the chemical and structural insight, can provide design rules for beneficial interfaces, an essential aspect for developing long-lasting energy storage systems.