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

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Current lithium-ion batteries face limitations in performance, safety, and cost.
• Next-generation batteries utilizing "beyond-Li" ions, particularly multivalent ions, are hindered by a poor understanding of their solid-state ion conduction.
• Developing advanced battery technologies requires exploring new materials and ion conduction mechanisms.

Purpose of the Study:

• To introduce a novel ligand-assisted ion conduction mechanism in M M PS₃-based solid host crystals.
• To enable ambient temperature superionic conductivity for various next-generation mobile ions.
• To investigate the influence of host structure, mobile ions, and coordinating ligands on ionic conductivity.

Main Methods:

• Synthesis of ligand-coordinated ions within M M PS₃ (M = Mn, Cd) solid host crystals.
• Investigation of ionic conductivity using pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy.
• Analysis of ion migration mechanisms, distinguishing between hopping and vehicular transport.

Main Results:

• Ligand coordination significantly increased interlayer spacing and screened charge-dense ions, facilitating ion migration.
• Ambient temperature superionic conductivity was achieved in M M PS₃-based solids with ligand-assisted conduction.
• PFG-NMR revealed a hopping conduction mechanism involving cations moving between H₂O molecules.

Conclusions:

• Ligand-assisted solid-state ionic conductivity is strongly influenced by cation charge density, diffusion channel size, and charge screening.
• The modular system allows for tailoring to specific battery applications and probing fundamental conduction principles.
• This research provides insights for designing novel solid-state ionic conductors, especially for multivalent ions, and M M PS₃ frameworks may serve as universal solid-state electrolytes.