Phonon transport in layered NaMnO2: Roles of interlayer electrostatic coupling and Jahn–Teller distortions

Sodium-ion batteries offer a sustainable alternative to lithium-based systems, but their safety and performance can be affected by inadequate thermal management during high-rate operation. Here, we present a first-principles investigation of lattice thermal transport in representative layered NaxMnO2 structural models, including the fully desodiated δ-MnO2 limit (x=0), an intermediate-composition O3′-Na0.5MnO2 model (x=0.5), and fully sodiated O3′-NaMnO2 and P2′-NaMnO2 polymorphs (x=1). Using the Boltzmann transport equation combined with the Wigner transport formalism, we reveal pronounced variations in both the magnitude and anisotropy of lattice thermal conductivity among these structural models. Relative to desodiated δ-MnO2, Na+ insertion redistributes charge and strengthens electrostatic interactions between the inserted Na+ layer and adjacent oxygen layers, thereby enhancing out-of-plane phonon transport. Meanwhile, the Mn3+-associated Jahn–Teller distortion softens selected in-plane Mn–O linkages and suppresses the corresponding in-plane thermal transport. These structural changes modify phonon dispersions, group velocities, and mean free paths, resulting in a substantial reduction in thermal conductivity anisotropy in the sodiated models. Our results clarify how Na content, interlayer interactions, and Jahn–Teller distortions jointly regulate anisotropic phonon transport in layered manganese oxides, providing insight relevant to thermal management in sodium-ion battery cathodes.