Li+ and Na+-ion conductors not only control the performance of all-solid-state-batteries but are also key components in large-scale metal-air, metal-sulfur, and alkali-redox flow batteries. Therefore, designing new and optimizing known ion conductors is crucial for enabling large-scale energy storage systems with high rate performance. The redevelopment of the crystal chemical bond valence approach into our energy-scaled “bond valence site energy” method  allows for computationally cheap predictions of ion migration pathways and migration barriers from static structure models and thus for high-throughput screening of wide ranges of candidate compounds as alkali ion or mixed conductors with balanced conductivity and stability. As a transferable effective forcefield for MD simulations it helps to analyze ion transport mechanisms, as exemplified here by a discussion of differences between alkali ion migration in superionic Li10GeP2S12 and Na10GeP2S12, explaining why the latter is, despite contrary predictions from ab initio MD simulations, only a moderate Na+ conductor. To overcome fundamental limitations of two-body forcefields, it will also be discussed how the approach can be augmented to an EAM-type multibody forcefield with bond valence sum-based embedding function.
As the ionic conductivity in mixed conductors also controls the achievable rate performance of insertion electrode materials, we extended our combined ab initio and empirical bond valence analyses to alkali-ion cathode material structures, demonstrating a simple structure property relationship that yields from the structure a quantitative prediction of the characteristic (dis)charge rate up to which a material (with given particle size) can be expected to deliver high capacity.
Experimentally we aim to establish rationally optimized processing for solid electrolytes and electrode materials by in situ X-ray or neutron monitoring of the formation process. Thereby we not only achieve phase pure high performance materials with well-controlled dopant contents in a cost and energy-efficient way, but provide deeper understanding of the formation mechanisms and kinetics of the desired phase as well as of potential impurities. We tested our predictions by the realization of all solid state Na+-ion batteries with high rate performance at room temperature  and of high energy efficiency aqueous Li-air batteries (LABs) using scalable fast-ion conductor membranes.[5,6]
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