A prerequisite for the realization of solid-state batteries is the development of highly conductive solid electrolytes. Li3PS4 is the archetypal member of the highly promising thiophosphate family of Li-ion conductors. Despite a multitude of investigations into this material, the underlying atomic-scale features governing the roles of and the relationships between cation and anion dynamics, in its various temperature-dependent polymorphs, are yet to be fully resolved. On this basis, we provide a comprehensive molecular dynamics study to probe the fundamental mechanisms underpinning fast Li-ion diffusion in this important solid electrolyte material. We first determine the Li-ion diffusion coefficients and corresponding activation energies in the temperature-dependent γ, β, and α polymorphs of Li3PS4 and relate them to the structural and chemical characteristics of each polymorph. The roles that both cation correlation and anion libration play in enhancing the Li-ion dynamics in Li3PS4 are then isolated and revealed. For γ- and β-Li3PS4, our simulations confirm that the interatomic Li–Li interaction is pivotal in determining (and restricting) their Li-ion diffusion. For α-Li3PS4, we quantify the significant role of Li–Li correlation and anion dynamics in dominating Li-ion transport in this polymorph for the first time. The fundamental understanding and analysis presented herein is expected to be highly applicable to other solid electrolytes where the interplay between cation and anion dynamics is crucial to enhancing ion transport.

The fluoride ion battery (FIB) is a promising post-lithium ion battery chemistry owing to its high theoretical energy density and the large elemental abundance of its active materials. Nevertheless, its utilization for room-temperature cycling has been impeded by the inability to find sufficiently stable and conductive electrolytes at room temperature. In this work, we report the use of solvent-in-salt electrolytes for FIBs, exploring multiple solvents to show that aqueous cesium fluoride exhibited sufficiently high solubility to achieve an enhanced (electro)chemical stability window (3.1 V) that could enable high operating voltage electrodes, in addition to a suppression of active material dissolution that allows for an improved cycling stability. The solvation structure and transport properties of the electrolyte are also investigated using spectroscopic and computational methods.

Multidentate neutral amine ligands play vital roles in coordination chemistry and catalysis. In particular, these ligands are used to tune the reactivity of Group-1 metal reagents, such as organolithium reagents. Most, if not all, of these Group-1 metal reagent-mediated reactions occur in solution. However, the solution-state coordination behaviors of these ligands with Group-1 metal cations are poorly understood, compared to the plethora of solid-state structural studies based on single-crystal X-ray diffraction (SCXRD) studies. In this work, we comprehensively mapped out the coordination modes with Group-1 metal cations for three multidentate neutral amine ligands: tridentate 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 TACN), tetradentate tris[2-(dimethylamino)ethyl]amine (Me 6 Tren), and hexadentate N,N′,N″-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN). The macrocycles in the Me 3 TACN and DETAN are identified as the rigid structural directing motif, with the sidearms of DETAN providing flexible “on-demand” coordination sites. In comparison, the Me 6 Tren ligand features more robust coordination, with the sidearms less likely to undergo the decoordinating–coordinating equilibrium. This work will provide a guidance for coordination chemists in applying these three ligands, in particular, the new DETAN ligand to design metal complexes which suit their purposes.

Although polycrystalline solid electrolytes are central to the utilization of solid- state batteries with lithium metal anodes, lithium dendrite formation and reduced Li-ion conductivity at their grain boundaries remain primary concerns. Given that experimental studies on polycrystalline materials are notoriously difficult to perform and interpret, computational techniques are invaluable for providing insight at the atomic scale. Here, we carry out first-principles calculations on representative grain boundaries in three important Li-based solid electrolyte families, namely, an anti-perovskite oxide, Li3OCl, a thiophosphate, Li3PS4, and a halide, Li3InCl6, to demonstrate the significantly different impacts that grain boundaries have on their electronic structure, ion conductivity and correlated ion transport. Our results show that even when grain boundaries do not significantly impact ionic conductivity, they can still strongly perturb the electronic structure and contribute to undesirable electrical conductivity and potential lithium dendrite propagation. We also illustrate, for the first time, how cor- related motion, including the so-called paddle-wheel mechanism, which has so far only been considered for the bulk, can vary substantially at grain boundaries. Our findings reveal the dramatically different behaviour of solid electrolytes at the grain boundary compared to the bulk and its potential consequences and benefits for the design of solid-state batteries.

Although polycrystalline solid electrolytes are central to the utilization of solid- state batteries with lithium metal anodes, lithium dendrite formation and reduced Li-ion conductivity at their grain boundaries remain primary concerns. Given that experimental studies on polycrystalline materials are notoriously difficult to perform and interpret, computational techniques are invaluable for providing insight at the atomic scale. Here, we carry out first-principles calculations on representative grain boundaries in three important Li-based solid electrolyte families, namely, an anti-perovskite oxide, Li3OCl, a thiophosphate, Li3PS4, and a halide, Li3InCl6, to demonstrate the significantly different impacts that grain boundaries have on their electronic structure, ion conductivity and correlated ion transport. Our results show that even when grain boundaries do not significantly impact ionic conductivity, they can still strongly perturb the electronic structure and contribute to undesirable electrical conductivity and potential lithium dendrite propagation. We also illustrate, for the first time, how cor- related motion, including the so-called paddle-wheel mechanism, which has so far only been considered for the bulk, can vary substantially at grain boundaries. Our findings reveal the dramatically different behaviour of solid electrolytes at the grain boundary compared to the bulk and its potential consequences and benefits for the design of solid-state batteries.