Thermal and ionic conductivity studies of lithium aluminum germanium phosphate solid-state electrolyte

• Thermal conductivity of two different LAGP solid electrolytes was measured.
• Wiedemann–Franz law can't explain LAGP thermal conductivity temperature dependence.
• A contribution of the mobile ions to the thermal transport might occur.

Two different compositions of lithium aluminum germanium phosphate glass–ceramics (LAGP) were prepared and investigated as candidate materials for solid-state electrolytes in Li-ion batteries. The thermal and the ionic conductivity behavior of these two different LAGP compositions were investigated. LAGP glasses were prepared using the melt-quench-method. Glass–ceramic samples were obtained from the prepared glasses via two different methods: powder sintering and bulk glass heat-treatment. The ionic conductivity was measured using complex impedance spectroscopy while the thermal diffusivity was measured using a Laser flash apparatus. The thermo-physical properties were studied using differential scanning calorimetry. X-ray diffraction and scanning electron microscopy were used to investigate the crystal structure and the microstructure. The sample with higher ionic conductivity had also shown higher thermal conductivity in the two different studied LAGP compositions. Moreover, the thermal conductivity was depending on the microstructure and density of the samples. Finally, the temperature dependence of the thermal conductivity could not be explained by a single mechanism or by the Wiedemann–Franz law. Therefore, a contribution of the mobile ions to the thermal transport might probably occur.