Modular MPS3-Based Frameworks for Superionic Conduction of Monovalent and Multivalent Ions

Next-generation batteries based on more sustainable working ions could offer improved performance, safety, and capacity over lithium-ion batteries, while also decreasing the cost. Development of next-generation battery technology using "beyond-Li" mobile ions is limited, in part, due to a lack of understanding of solid state conduction of these ions. Next-generation mobile ions tend to have relatively low mobility in solids due to: (1) larger ionic radii (Na+, K+, Ca2+), which limit the accessible migration pathways, and/or (2) higher charge densities (Mg2+, Zn2+, Al3+, which result in strong electrostatic interactions within the solid. Here, we introduce ligand-coordinated ions into MPS3-based solid host crystals (M = Mn, Cd) to simultaneously increase the size of the bottlenecks within the migration pathway and screen the charge-dense ions. We employ X-ray diffraction, thermogravimetric analysis, inductively coupled plasma mass spectrometry, scanning electron microscopy, energy dispersive X-ray spectroscopy, solid state magic angle spinning nuclear magnetic resonance spectroscopy, pulsed field gradient nuclear magnetic resonance spectroscopy, density functional theory quantum mechanics, and electrochemical impedance spectroscopy to probe the ionic mobility, structural and chemical changes in the MPS3 materials after ion exchange. We show that the inclusion of coordinating ligands enables ambient temperature superionic conductivity of various next-generation mobile ions in an electronically-insulating MPS3-based solid. These ion-intercalated MPS3-based frameworks not only enable deeper understanding of ligand-coordination in solid state ionic conduction, but could potentially serve as a universal solid state electrolyte for various next-generation battery chemistries.