In hot pursuit: tracking ionic and phononic heat carriers in Li₃OCl across temperatures

Although lithium-rich antiperovskite Li₃OCl is a promising candidate for solid-state battery electrolytes, its thermal transport properties—especially at elevated temperatures—remain poorly understood. In this work, we employ Green–Kubo equilibrium molecular dynamics with machine-learned interatomic potentials, and ab initio anharmonic lattice dynamics and a transport framework that captures both particle-like (phononic) and wave-like (diffusive) behaviors. This combined approach enables the prediction of thermal conductivity across a broad temperature range. We disentangle the contributions of lattice vibrations, ionic transport, and their coupling, revealing distinct roles for particle- and wave-like heat carriers' contributions to lattice vibrations. While Li₃OCl retains a crystalline structure throughout, thermal transport below ∼1100 K is dominated by the particle-like phonon conduction. At higher temperatures, significant Li⁺ migration emerges in the quasi-liquid state, introducing a particle advection heat transport component. Simultaneously, strong vibrations of the non-migrating lithium atoms promote the wave-like, glassy contribution to vibrational heat conduction. Together, these findings offer a comprehensive understanding of thermal transport in Li₃OCl and provide quantitative insights for addressing thermal management in solid-state battery systems.