Dr. Xi Chen, Associate Professor of Electrical and Computer Engineering at the Marlan and Rosemary Bourns College of Engineering, University of California, Riverside, has led a research team in uncovering why a key solid-state battery material remains remarkably cool during operation. Their work focuses on lithium lanthanum zirconium tantalum oxide, commonly known as LLZTO, a ceramic solid electrolyte considered promising for next-generation lithium batteries. The study, provides critical insights into how the material’s atomic structure influences heat transport, offering potential pathways to safer and more energy-dense batteries.
Wang, Y., Su, Y., Carrete, J., Zhang, H., Wu, N., Li, Y., Li, H., He, J., Xu, Y., Guo, S., Cai, Q., Abernathy, D. L., Williams, T., Kravchyk, K. v., Kovalenko, M. v., Madsen, G. K. H., Li, C., & Chen, X. (2025). Origin of Intrinsically Low Thermal Conductivity in a Garnet-Type Solid Electrolyte: Linking Lattice and Ionic Dynamics with Thermal Transport. PRX Energy, 4(3), 033004. https://doi.org/10.1103/6wj2-kzhh
Solid-state batteries use a solid electrolyte layer to separate the cathode and anode, replacing the liquid electrolytes used in conventional lithium-ion batteries. This change promises higher energy density and reduced risk of overheating or fire. However, until now, the mechanisms underlying LLZTO’s unusually low thermal conductivity were not fully understood. This property is essential because heat buildup during charging and discharging can degrade performance, shorten battery life, or even trigger thermal runaway, a chain reaction that can lead to fires or explosions. Understanding how LLZTO naturally impedes heat flow is critical for designing batteries that store more energy safely.
Dr. Xi Chen, from the University of California, Riverside stated,
“By linking lattice vibrations and ionic movement to thermal behavior, it is possible to design materials that not only conduct ions efficiently but also manage heat safely. We’re looking at the big picture; how atomic-scale dynamics influence macroscopic behavior in energy systems.
The team, including graduate student Yitian Wang as first author, grew single crystals of LLZTO using a floating-zone method. Single crystals provide a pristine structural model compared to polycrystalline samples, which contain many small grains that scatter heat and obscure intrinsic properties. The experiments revealed that LLZTO’s thermal conductivity is as low as 1.59 watts per meter-kelvin, roughly 250 times lower than copper. This result indicates that the low thermal conductivity is an inherent feature of the material, not a consequence of defects or impurities.
To investigate the underlying cause, the researchers combined neutron scattering experiments at Oak Ridge National Laboratory with advanced computational simulations. These analyses showed that the unique vibrational behavior of atoms within the crystal lattice is responsible for limiting heat transport. LLZTO contains numerous optical phonon modes, where atoms vibrate out of phase with their neighbors. These optical vibrations interact with acoustic phonons, which primarily carry heat, scattering them and reducing the material’s ability to conduct thermal energy.
In addition, LLZTO exhibits significant anharmonicity, meaning its atomic vibrations deviate from ideal harmonic motion. This property is linked to the mobility of ions within the material and suggests that traditional models of thermal transport may not fully explain its behavior. The combination of optical phonon scattering and anharmonicity provides a detailed atomic-level explanation for the material’s low thermal conductivity, offering researchers new ways to predict temperature profiles inside batteries and design more efficient thermal management strategies.
The findings have practical implications for battery engineering. By understanding how LLZTO impedes heat flow, engineers can develop solid-state batteries that operate at higher energy densities without overheating. This knowledge is particularly valuable for applications where safety and compact energy storage are critical, including electric vehicles, portable electronics, and aerospace systems.
Future research may explore similar solid electrolytes, aiming to identify materials that combine high ionic conductivity with intrinsically low thermal conductivity. The team also anticipates investigating ways to tailor LLZTO’s atomic structure to optimize its thermal and electrochemical properties for specific battery applications. By linking atomic-scale behavior to macroscopic performance, the research opens new avenues for designing safer and more powerful energy storage systems.
Dr. Chen emphasizes that the study demonstrates the importance of understanding atomic dynamics in materials science. By connecting lattice vibrations and ionic movement to heat transport, engineers can create materials that are both highly conductive for ions and effective at managing thermal energy. This approach represents a critical step toward the next generation of solid-state batteries, where performance and safety can coexist without compromise.
The research conducted at UC Riverside highlights the potential of interdisciplinary collaboration, combining experimental techniques, computational modeling, and materials engineering to address complex challenges in energy storage. The insights from LLZTO provide a foundation for continued innovation in solid-state battery design, with the ultimate goal of producing devices that deliver higher energy density, longer lifespans, and improved operational safety.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
