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Summary Tremendous interest in solid-state devices has prompted the development of descriptors that can be utilized to develop better materials. Previous work mostly focused on the static structure, while discovery of the interplay between cation mobility and anion dynamics can also provide a powerful descriptor. Here, we demonstrate that [PS4] rotation is remarkably facile in fast ion conductors β-Li3PS4 and its Si-substituted analog, Li3.25Si0.25P0.75S4, whereas it is absent in the non-conductive phase, γ-Li3PS4. Phonon calculations identify the increased entropy upon substitution of Si for P as the origin of the stabilization of the high-temperature phase (β-Li3PS4) at room temperature. Joint-time correlation analysis and power spectra reveal that [PS4]/[SiS4] anion rotational dynamics are coupled to and greatly enhance cation diffusion via the paddle-wheel effect by widening the bottleneck for Li+-ion transport. These findings shed light on the critical role of anion dynamics and can serve as a general guideline for the design of new conductors.

All-solid-state Li-ion batteries (ASSBs), considered to be potential next-generation energy storage devices, require solid electrolytes (SEs). Thiophosphate-based materials are popular, but these s...

We report the first in situ variable temperature neutron powder diffraction (NPD) study of the solid-state ion conductor Li3PS4 which delineates the transitions between its three polymorphs (γ → β → α) and determines their crystalline Li-sublattices. They are compared to those of nanoporous β-Li3PS4, and β′-type Si-substituted Li3.25Si0.25P0.75S4. Importantly, Rietveld refinement of the NPD data elucidates the crystal structure of the high-temperature α-Li3PS4 polymorph for the first time and shows that it crystallizes in the Cmcm space group. The lithium diffusion pathways of both the bulk β and α polymorphs are evaluated using the maximum entropy method and bond valence site energy calculations, revealing that the structure of α-Li3PS4 favors facile 3D conduction, supported mainly by its bcc S-sublattice. The variable temperature in situ NPD study of nanoporous β-Li3PS4 identifies the presence of an amorphous organic component that is only completely removed upon transformation to the α-phase at elevated temperature, and which may play a role in stabilizing this material at room temperature. Si-substitution of Li3PS4 not only stabilizes the β′-Li3.25Si0.25P0.75S4 phase at room temperature but also prevents phase transformation to the α polymorph upon heating owing to its larger lattice volume.

Lithium thioborates are promising fast Li-ion conducting materials, with similar properties to their lithium thiophosphate counterparts that have enabled the development of solid-state Li-ion batteries. By comparison, thioborates have scarcely been developed, however, offering new space for materials discovery. Here we report a new class of lithium thioborate halides that adopt a so-called supertetrahedral adamantanoid structure that houses mobile lithium ions and halide anions within interconnected 3D structural channels. Investigation of the structure using single-crystal XRD, neutron powder diffraction, and neutron PDF reveals significant lithium and halide anion disorder. The phases are non-stoichiometric, adopting slightly varying halide contents within the materials. These new superadamantanoid materials exhibit high ionic conductivities up to 1.4 mS cm-1 , which can be effectively tuned by the polarizability of the halide anion within the channels.

Solid electrolytes are the foundation of all-solid-state batteries (ASSB) and have the potential to provide improved safety and higher energy density than existing liquid battery systems. In the important search for new lithium ion conductors with fast ionic conductivity and good mechanical properties, thiophosphates are a particularly promising class of materials. The first experimental elucidation of new lithium ion conductors in the Li1+2xZn1-xPS4 (LZPS) solid solution whose existence had been predicted by theory is reported herein. Using neutron and synchrotron x-ray powder diffraction together with electrical impedance, and Raman studies, we resolve their crystalline nature and correlate this with ionic conductivity upon increasing the lithium/zinc ratio. We show that the materials exhibit high experimental ionic conductivities - up to 8 × 10-4 S·cm-1 - and reveal the nature of likely pathways for lithium ion conduction.

We report a new sodium superionic conductor, Na11Sn2PS12, that crystallizes in an unprecedented three-dimensional structure type and exhibits an ionic conductivity of 1.4 mS cm−1, with a very low activation energy barrier for Na-ion mobility of 0.25 eV. A combination of structural elucidation via single crystal X-ray diffraction and ab initio molecular dynamics simulations show that Na+-ion conduction pathways flow through equi-energetic sodium–sulfur octahedra interconnected by partial vacancy cross-over sites in all crystallographic dimensions, providing an understanding of the underlying isotropic 3D fast-ion conduction in this material.

The lithium-sulfur battery is a compelling energy storage system because its high theoretical energy density exceeds Li-ion batteries at much lower cost, but applications are thwarted by capacity decay caused by the polysulfide shuttle. Here, proof of concept and the critical metrics of a strategy to entrap polysulfides within the sulfur cathode by their reaction to form a surface-bound active redox mediator are demonstrated. It is shown through a combination of surface spectroscopy and cyclic voltammetry studies that only materials with redox potentials in a targeted window react with polysulfides to form active surface-bound polythionate species. These species are directly correlated to superior Li-S cell performance by electrochemical studies of high surface area oxide cathodes with redox potentials below, above, and within this window. Optimized Li-S cells yield a very low fade rate of 0.048% per cycle. The insight gained into the fundamental surface mechanism and its correlation to the stability of the electrochemical cell provides a bridge between mechanistic understanding and battery performance essential for the design of high performance Li-S cells.