Temperature dependence of structure and ionic conductivity of LiTa2PO8 ceramics

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American Chemical Society
LiTa2PO8 has recently been reported as a new fast Li-ion conducting structure type within the series of Lix(MO6/2)m(TO4/2)n polyanion oxides. Here, we demonstrate the preparation of LiTa2PO8 by solid-state syntheses, clarify the temperature dependence of lithium distribution and ionic conductivity, and study the structural stability, densification, and achievable total conductivity as a function of sintering conditions synergizing experimental neutron and X-ray powder diffraction and electrochemical studies with computational energy landscape analyses and molecular dynamics simulations. A total room temperature conductivity of 0.7 mS cm-1 with an activation energy of 0.27 eV is achieved after sintering at 1323 K for 10 h. Spark plasma sintering yields high densification >98%, highly reproducible bulk conductivities of 2.8 mS cm-1, in agreement with our bond valence site energy-based pathway predictions, and total conductivities of 0.6 mS cm-1 within minutes. Powder diffraction studies from 3 to 1273 K reveal a reversible flipping of the monoclinic angle from above to below 90° close to room temperature as a consequence of rearrangements of the mobile ions that change the detailed pathway topology. A consistent model of the temperature-dependent Li redistribution, conductivity anisotropy, and transport mechanism is derived from a synopsis of diffraction experiments, experimental conductivity studies, and simulations. Due to the limited electrochemical window of Lix(TaO6/2)2(PO4/2)1 (LTPO), a direct contact with Li metal or high voltage cathode materials leads to degradation, but as demonstrated in this work, semi-solid-state batteries, where LTPO is protected from direct contact with lithium by organic buffer layers, achieve stable cycling. © 2022 American Chemical Society
Temperature dependence, Ionic conductivity, Lithium, Tantalum, Polonium, Sintering, Diffraction, Electrolytes
Dai, R., Avdeev, M., Kim, S.-J., Prasada Rao, R., & Adams, S. (2022). Temperature Dependence of Structure and Ionic Conductivity of LiTa2PO8 Ceramics. Chemistry of Materials, 34(23), 10572-10583. doi:10.1021/acs.chemmater.2c02640