Solid-state fast ionic conductors are of great interest due to their application potential enabling the development of safer high-performance energy and conversion systems ranging from batteries through supercapacitors to fuel cells, electrolyzers, and novel neuromorphic devices. However, identifying fast ion conductors has remained a slow trial-and-error search process. High-throughput computational screening methods such as our bond valence site energy method can significantly accelerate this materials design, but their implementation not only needs to be computationally efficient and dependable but also simple to be used by experimentalists in order to find widespread usage for guiding experimental efforts to promising classes of candidate materials. To bridge the current gap between computational method developers and application-oriented users, we combine the computationally low-cost bond valence site energy calculations in our softBV software tool using a new automated pathway analysis toolthe bond valence pathway analyzer (BVPA). The integration of BVPA gives rapid comprehensive access to and simplifies the visualization of the desired information on the characteristics of ion transport properties in candidate materials. Examples for the main application of identifying suitable structure types for fast ion transport as solid electrolytes or mixed conducting electrode materials with high-rate capability are given. A new dopant predictor further simplifies defect engineering of the candidate systems by automatically suggesting suitable substitutional dopants for each site in the structure based on a new machine-learned approach.

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LiTa2PO8 has recently been reported as a new fast Li-ion conducting structure type within the series of Li x (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 Li x (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.

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