Hybrid Material Concepts for Thiophosphate-Based Solid-State Batteries

Abstract

Solid-state batteries (SSBs) could replace conventional lithium-ion batteries due to the possibility of increasing the energy density of the cells by using lithium metal as the anode material.[1] Among the many electrolyte candidates for lithium SSBs, the lithium thiophosphates are particularly interesting due to their high ionic conductivities at room temperature (>1 mS/cm). However, the (electro)chemical stability of these solid electrolytes is limited and not fully compatible with state-of-the-art high-potential cathode active materials[2] or the lithium metal anode.[3] At the cell level, the formation of interparticle voids between the various battery components (solid electrolyte, cathode active material, anode material, additives, decomposition interphases) hinder the net transport during cycling. To address the latter electro-chemo-mechanical challenges, we are exploring hybrid material approaches, in which we combine established materials (solid electrolytes, liquid electrolytes and/or polymer additives) with state-of-the-art cathode active materials and test their electrochemical performance in solid-state battery (half-)cells. Such cycling results are complimented by detailed electrochemical transport studies in symmetrical cells using DC polarization and electrochemical impedance spectroscopy, including transmission-line modeling. ex.situ chemically-specific spectroscopic methods are used to support our hypotheses and interpretation of the electrochemical results. Taken together, we attain a better picture on the positive (or negative) role hybrid materials play in SSBs. In this talk, we will showcase two hybrid systems, namely ionic liquid/thiophosphate lithium hybrid electrolytes and conductive polymers additives in NMC-based catholyte composites for Li6PS5Cl cells. The first part of the talk we will discuss the results in which we evaluate the performance of liquid electrolyte-solid electrolyte materials against lithium metal using galvanostatic electrochemical impedance spectroscopy. In the second part, we elucidate the partial ionic and electronic transport in polymer electrolyte-Li6PS5Cl-NMC catholytes as a function of polymer content using impedance spectroscopy and its effect in the cycling performance, both the stability as well as the magnitude of the discharge capacities. These systems serve as a good starting point for the further development and incorporation of hybrid materials in SSBs.Literature: [1] W. G. Zeier and J. Janek Nature Energy, 2016, 1, 16141. [2] G.F. Dewald, S. Ohno, M.A. Kraft, R. Kroever, P. Till, N.M. Vargas-Barbosa, J. Janek, W.G. Zeier Chem. Mater. 2019, 31, 8328. [3] L. M. Riegger, R. Schlem, J. Sann, W. G. Zeier, J. Janek, Angew. Chem. Int Ed 2021, 60, 6718. Figure 1