In Situ Investigation of Interfacial Degradation Mechanisms in Next-Generation Batteries

Improving the energy density and cycling stability of battery systems are inevitable for fulfilling the targeted climate goals.¹ Interfaces between different materials, which are present in all types of lithium-based batteries, play a crucial role in reaching these goals. At these interfaces, degradation and charge-transfer resistances occur. When the degradation mechanism and the fundamentals of ion transport across the interfaces are distinctively understood, the development of proper countermeasures can sustainably improve future batteries.<br/>Besides electrode–electrolyte interfaces, those between different types of electrolytes—which we call here “heteroionic” interfaces—are much less investigated, but equally as important. They occur, for example, in hybrid all-solid-state batteries, where the malleability and ionic conductivity of sulfide-based solid electrolytes (SEs) is combined with the chemical stability of oxide-based ones. Composites of polymer electrolytes (PEs) with added SE particles for improved ionic conductivity also involve heteroionic interfaces. And lastly, liquid electrolytes (LEs) are often applied for improved contact between electrodes and SEs as well as formation of a stable SEI on lithium metal, preventing degradation during contact to the SE. Additionally, SE separators can prevent detrimental chemical cross-talk in next-generation Li–S or Li–O₂ batteries and dendrite propagation.²<br/>Herein, we analyze charge-transfer across heteroionic interfaces and interfacial degradation for multiple different SEs using a combined approach of state-of-the-art in situ and ex situ techniques. Thereby, the formation of an interphase of degradation products (solid/liquid electrolyte interphase, SLEI) is detected on the SE surface, mainly contributing to the high interfacial resistance. SLEI formation is investigated by in situ neutron reflectometry and quartz crystal microbalance studies, while its resistance is monitored in situ via time-resolved four-point impedance spectroscopy. Combined with surface analysis and depth profiling by X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, and atomic force microscopy, an in-depth understanding of the composition and formation mechanism of the interphase is obtained.^3–5<br/>Evaluating different combinations of LE and SE, the material selection is optimized and the importance of surface morphology highlighted. Consequently, NASICON-based SEs are found to exhibit lower interphase resistances than LiPON when combined with ethereal LEs commonly used in next-generation batteries.^2,5<br/>Literature:<br/>[1] J. Janek, W. G. Zeier, <i>Nat. Energy</i> <b>2016</b>, <i>1</i>, 16141.<br/>[2] M. Weiss, F. J. Simon, M. R. Busche, T. Nakamura, D. Schröder, F. H. Richter, J. Janek, <i>Electrochem. Energ. Rev.</i> <b>2020</b>, <i>3</i>, 221.<br/>[3] M. R. Busche, T. Drossel, T. Leichtweiss, D. A. Weber, M. Falk, M. Schneider, M.-L. Reich, H. Sommer, P. Adelhelm, J. Janek, <i>Nat. Chem.</i> <b>2016</b>, <i>8</i>, 426.<br/>[4] M. Weiss, B.-K. Seidlhofer, M. Geiß, C. Geis, M. R. Busche, M. Becker, N. M. Vargas-Barbosa, L. Silvi, W. G. Zeier, D. Schröder et al., <i>ACS Appl. Mater. Interfaces</i> <b>2019</b>, <i>11</i>, 9539.<br/>[5] M. R. Busche, M. Weiss, T. Leichtweiss, C. Fiedler, T. Drossel, M. Geiss, A. Kronenberger, D. A. Weber, J. Janek, <i>Adv. Mater. Interfaces</i> <b>2020</b>, 2000380.