UC Riverside

All-solid-state batteries replace flammable liquid electrolytes with inorganic solid electrolytes, yet the thermal properties of these ion conductors remain less understood than their ionic conductivity. Because solid electrolytes form continuous heat pathways between electrodes, their thermal conductivity (κ) governs temperature profiles, degradation, and cycling safety. This dissertation examines thermal transport and lattice dynamics in oxide solid electrolytes and explains low, glass-like heat transport in ion conductors.Single-crystal Li6.5La3Zr1.5Ta0.5O12 (LLZTO) was grown by floating zone method. Thermal measurements show an intrinsically low room-temperature κ of 1.59(33) Wm−1 K −1 . Inelastic neutron scattering observes acoustic phonons, while first-principles calculations reproduce the spectra and reveal dense optical modes with acoustic-optical avoided crossings near 7 meV. Quasielastic neutron scattering reveals fast local Li hopping, connecting mobile-ion dynamics with heat-suppressing lattice dynamics. A two-channel analysis links weak temperature dependence to diffuson-mediated transport.Polycrystalline LLZTO exhibits a low-temperature κ peak near 50 K, followed by weak temperature dependence above 200 K. Thermal expansion and mechanical testing yield a Grüneisen parameter of 1.63(4), quantifying strong lattice anharmonicity. Aging in air increases κ by ∼75% at room temperature due to Li2CO3 formation and modified thermal boundary resistance.The perovskite lithium-ion conductor Li3/8Sr7/16Hf1/4Ta3/4O3 (LSHT) displays glass-like thermal transport, with κ = 1.7(5) Wm−1 K −1 at room temperature. The data indicate strong disorder-driven scattering and a significant diffuson contribution, showing similar heat-transport suppression in perovskites.The NaSICON-type electrolyte Na3Zr2Si2PO12 (NZSP) has a Debye temperature of 370 K, sound velocity of 2962 ms−1 , and room-temperature κ of 1.01(6) Wm−1 K −1 . Its κ shows a low-temperature peak near 95 K and a plateau above ∼200 K. Its Grüneisen parameter of 0.70 indicates intermediate anharmonicity relative to related NaSICON compositions.Together, these studies establish lattice-dynamics principles for thermal management and materials design in all-solid-state batteries, positioning solid electrolytes as a platform for studying and controlling heat transport.