Decoding Structural Disorder, Synthesis Methods, and Short- and Long-Range Lithium-Ion Transport in Lithium...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Lithium-ion conductivity in solid electrolytes is crucial for advanced battery technologies.
• Understanding the interplay between chemical composition, structural disorder, and ion dynamics is key to optimizing performance.
• Previous studies often link conductivity to simple site disorder, potentially overlooking other contributing factors.

Purpose of the Study:

• To disentangle the effects of site disorder and chemical composition on the ionic conductivity of Li_6- PS_5- Br₁₊ solid electrolytes.
• To investigate the influence of synthesis routes, specifically cooling methods, on structural and dynamic properties.
• To establish a more comprehensive understanding of the factors governing lithium-ion transport.

Main Methods:

• Synthesis of Li_6- PS_5- Br₁₊ (x = 0, 0.3, 0.5) with varying bromine content and cooling rates (slow-cooling vs. quench-cooling).
• Solid-state nuclear magnetic resonance (NMR) spectroscopy (7Li and 31P) to probe chemical environments and short-range ion dynamics.
• Neutron diffraction for structural analysis and electrochemical impedance spectroscopy (EIS) for long-range conductivity measurements.

Main Results:

• Cooling method significantly alters the 7Li and 31P environments, indicating effects beyond simple 4d site disorder.
• Configurational entropy (Sconf) serves as a better descriptor of structural disorder, correlating with phosphorus and lithium environment distortions.
• Increased short-range lithium-ion movement (via NMR) correlates with Sconf, but this relationship breaks down for long-range conductivity (via EIS) in quench-cooled samples.

Conclusions:

• Altering synthesis parameters, like cooling rate, profoundly changes the relationship between structural disorder and lithium dynamics.
• Chemical composition and descriptors of structural disorder are distinct factors influencing conductivity at different length scales.
• The study challenges the assumption that increased short-range diffusivity directly translates to increased long-range diffusivity, highlighting the role of lattice softness and phonon-ion interactions.