Revealing the Local Structure and Dynamics of the Solid Li Ion Conductor Li₃P₅O₁₄

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Fast Li ion-conducting solid electrolytes are crucial for all-solid-state batteries.
• Understanding structure-ionic mobility-function relationships is key to developing advanced battery materials.
• Ultraphosphate Li3P5O14 is a promising candidate for oxide-based Li ion conductors due to its conductivity and stability.

Purpose of the Study:

• To elucidate the local structure and Li ion dynamics in Li3P5O14 using multinuclear NMR and DFT.
• To establish structure-ionic mobility relationships for optimizing solid electrolyte performance.
• To experimentally verify proposed 3D Li diffusion pathways in Li3P5O14.

Main Methods:

• Multinuclear and multidimensional Nuclear Magnetic Resonance (NMR) spectroscopy (6Li and 31P MAS NMR, MAS variable-temperature line narrowing, spin-alignment echo, relaxometry, 6Li-6Li exchange spectroscopy).
• Density Functional Theory (DFT) calculations.
• Analysis of diffusion-induced spin-lattice relaxation data.

Main Results:

• Comprehensive assignment of ultraphosphate layers and Li6O16 26- chains using 31P and 6Li MAS NMR with DFT.
• Identification of specific P sites with lower chemical shift anisotropy, indicating bridging phosphate bonding.
• Experimental verification of 3D Li diffusion pathways, with Li1 and Li5 sites identified as the most mobile.
• NMR exchange spectroscopy revealed Li ion exchange pathways between Li6O16 26- chains and through P12O36 12- rings.

Conclusions:

• Detailed understanding of Li ion mobility pathways in Li3P5O14 has been achieved.
• The study provides insights into optimizing fast ion conduction in solid electrolytes.
• This work paves the way for developing improved materials for high-performance all-solid-state batteries.