All-solid-state rechargeable lithium-ion batteries (AS-LIBs) are attractive power sources for electrochemical applications due to their potentiality in improving safety and stability over conventional batteries with liquid electrolytes. Finding a solid electrolyte with high ionic conductivity and compatibility with other battery components is a key factor in raising the performance of AS-LIBs. In this work, we prepare argyrodite-type Li 6 PS 5 X (X = Cl, Br, I) using mechanical milling followed by annealing. X-ray diffraction characterization reveals the formation and growth of crystalline Li 6 PS 5 X in all cases. Ionic conductivity of the order of 7×10 −4 S cm −1 in Li 6 PS 5 Cl and Li 6 PS 5 Br renders these phases suitable for AS-LIBs. Joint structure refinements using high-resolution neutron and laboratory X-ray diffraction provide insight into the influence of disorder on the fast ionic conductivity. Besides the disorder in the lithium distribution, it is the disorder in the S 2− /Cl − or S 2− /Br − distribution that we find to promote ion mobility, whereas the large I − cannot be exchanged for S 2− and the resulting more ordered Li 6 PS 5 I exhibits only a moderate conductivity. Li + ion migration pathways in the crystalline compounds are modelled using the bond valence approach to interpret the differences between argyrodites containing different halide ions.

Due to their favourable combination of high ionic conductivity and stability versus elemental lithium, garnet-related lithium ion conductors Li 7 La 3 Zr 2 O 12 have raised strong interest for both all-solid-state batteries and as protective layers for anode materials. Here we study the correlation between structure and ion mobility in Li 7Àx La 3 (Zr 2Àx M x )O 12 (x ¼ 0, 0.25; M ¼ Ta 5+ , Nb 5+ ) combining Molecular Dynamics (MD) simulations, bond valence (BV) studies and experimental characterisation. In situ XRD demonstrates a tetragonal-to-cubic phase transition above 450 K for Li x La 3 Zr 2 O 12 . MD simulations using our new BV-based Morse-type force field reproduce static (lattice constants, thermal expansion, phase transition) and dynamic characteristics of this material. Simulations and structure refinements for the tetragonal phase accordingly yield an ordered Li distribution. The majority of Li fully occupies the 16f and 32g octahedral sites. Out of the two tetrahedral sites only the 8a site is fully occupied leaving the 16e tetrahedral sites with slightly higher site energy due to the tetragonal distortion vacant. For the cubic phase recent structural studies either suggest a major Li + redistribution to nearly fully occupied tetrahedral sites and distorted octahedral sites with a low occupancy (which leads to unphysically short Li-Li distances) or suggest the existence of additional Li sites. MD simulations however show that the lithium distribution just above the phase transition closely resembles that in the tetragonal phase with only slightly more than 1/3 of the now equivalent tetrahedral 24d sites and almost half of the distorted octahedral 96h sites occupied, so that overly short Li-Li distances are avoided. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and by reducing local Li ordering. At higher temperatures Li is gradually redistributed to the tetrahedral sites that can be occupied up to a site occupancy factor of 0.56. BV pathway analysis and closely harmonizing Li trajectories demonstrate that the two partially occupied Li sites of similar site energy form a 3D network suitable for fast ion conduction. The simulated diffusion coefficient and its activation energy closely match the experimental conductivities. The degree of correlation of the vacancy-type Li + ion migration is analyzed in terms of the van Hove correlation function.

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In situ synchrotron X-ray diffraction study of the synthesis of solid-electrolyte Li1+xAlxGe2−x(PO4)3 (LAGP) from the precursor glass reveals that an initially crystallized dopant poor phase transforms into the Al-doped LAGP at 800 °C.

In the search for new solid electrolytes with favorable combinations of fast ionic conductivity and sufficient structural and electrochemical stability, we here explore lithium compounds containing multiple anions, in particular the combination of thiophosphate and halide anions. On the basis of computational screening using our bond valence site approach and DFT studies several lithium thiophosphate halides including Li 4 PS 4 I, Li 5 PS 4 Cl 2 , Li 7 P 2 S 8 I, and the new Li 15 (PS 4 )X 3 (X = Cl, Br) have been explored. Their properties are discussed based on both static bond valence site energy pathway models and empirical molecular dynamics simulations using a BVSE-based force field, introducing also a new algorithm to predict absolute ionic conductivities from the static BVSE pathway analysis. MD simulations show that both Li 4 PS 4 I and Li 5 (PS 4 )Cl 2 is found to undergo an order−disorder phase transition and thus Li 5 (PS 4 )Cl 2 should, contrasting to earlier predictions, not be a fast Li + ion conductor at room temperature. Similarly, Li 4 PS 4 I the ionic conductivity should not reach the previously predicted extraordinary room temperature values. The newly predicted thermodynamically stable cubic solid electrolyte Li 15 (PS 4 ) 4 Cl 3 was successfully prepared and characterized for the first time. Li 15 (PS 4 ) 4 Cl 3 crystallizes in space group I4̅ 3d. Aliovalent doping of Mg 2+ on Li + sites enhances ionic conductivity only slightly from 4 × 10 −8 S cm −1 to 2 × 10 −7 S cm −1 . Though the conductivity of Li 15 (PS 4 ) 4 Cl 3 does not reach a superionic level, it demonstrates that our computational approach can successfully predict a completely new classes of solid electrolytes. Beyond the specific class of compounds we also discuss the fundamental challenge that the high probability of order−disorder phase transitions in intrinsic ionic conductors poses to the predictability of room temperature ionic conductivity by extrapolations from high temperature simulations. Empirical simulations although less precise can provide substantial additional insight, as they can cover both more complex structure models and wider temperature ranges to eliminate the need for extrapolations.