US scientists find solid battery material moves lithium ions rapidly above 260°F

A promising solid battery material lets lithium ions move rapidly when heated above 260°F (400 K), according to a study of how the material behaves at the atomic scale.

Researchers examined lithium phosphorus sulfur chloride, known as Li₆PS₅Cl, using neutron scattering and computer simulations. Their findings show that vibrations in its crystal structure help ions pass through narrow openings and travel across the material.

The work offers a closer look at a challenge in solid-state batteries: moving ions quickly through a solid electrolyte.

The team used neutron scattering measurements at Oak Ridge National Laboratory’s Spallation Neutron Source to observe movement across a range of temperatures.

A solid with liquid-like ion movement

Electrolytes carry charged particles between a battery’s electrodes during charging and discharging. Liquid electrolytes generally allow ions to move more freely than solid ones, making ion flow a key consideration for solid-state battery development.

Li₆PS₅Cl belongs to a class of materials called superionic conductors. They retain a crystalline structure while allowing some ions to move in ways that resemble their movement through a liquid.

When the researchers heated Li₆PS₅Cl above 400 K, it entered a superionic state. Lithium ions could then hop quickly between stable positions in the crystal lattice, giving the solid a route for rapid ion transport.

The measurements also showed a change in the ions’ vibrational behavior as the material moved from a more crystal-like state toward a liquid-like one. That shift gave the team another way to examine what happens as ion mobility increases.

Vibrations open the bottlenecks

The ions’ movement depended on more than temperature alone. The researchers found that particular vibrations in the surrounding crystal framework helped lithium ions pass through narrow points along their route.

These openings, called diffusion bottlenecks, change as the structure vibrates. Their motion makes it easier for ions to jump from one lattice site to another and move longer distances.

To investigate the process, the team combined machine-learning simulations with two neutron scattering techniques.

Together, these methods linked changes in the material’s vibrations to changes in lithium-ion diffusion across different temperatures.

The result helps explain how a material can remain partly crystalline while still supporting fast, liquid-like ion movement. It also links two ways of studying ion transport: tracking particles as they diffuse and examining the vibrations of the lattice around them.

What it means for battery research

Understanding which vibrations assist ion movement could help researchers design solid electrolytes with better conductivity. The goal is a material that combines a large supply of mobile ions with chemical and thermal stability.

That combination could make solid electrolytes more useful in batteries, with potential benefits for charging speed and safety.

The study identifies a mechanism researchers can investigate further; it does not demonstrate those improvements in a finished battery. The findings may also inform work on other technologies that depend on fast ion movement, including fuel cells and computing systems.

The National Science Foundation (DMREF project), the U.S. Department of Energy(DOE) Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and the German Research Foundation partially funded the research.