High pressure typically enhances thermal conductivity by strengthening atomic interactions. However, PdS has recently been reported to exhibit an unusual pressure-induced suppression of thermal conductivity, which in turn leads to a remarkable enhancement in its thermoelectric performance at high pressure. These insights motivate the search for additional materials that exhibit anomalous thermal-transport behavior under high pressure. Here, we find that hydrostatic pressure induces an anomalous change in lattice thermal conductivity (${\kappa }_l$) in antifluorite structure ${\mathrm{Li}}_2\mathrm{Te}$ by density-functional theory and phonon Boltzmann-transport calculations. The lattice thermal conductivity decreases monotonically under pressure, dropping by 72% to $1.99\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 40 GPa compared to ambient conditions. This anomalous behavior arises from the broadened acoustic branches and the enlarged acoustic-optical (a-o) phonon gap under high pressure, which together intensify phonon scattering. The enhanced anharmonicity under pressure is evidenced by both flattened frozen-phonon potentials and enhanced Grüneisen parameters. This work establishes ${\mathrm{Li}}_2\mathrm{Te}$ as a prototypical system for pressure-mediated thermal-transport tuning and highlights phonon scattering as a critical design parameter for engineering materials.

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• Anharmonic lattice dynamics
• Lattice thermal conductivity
• Pressure effects
• Density functional calculations