Amorphous Li-ion conductors are important solid-state electrolytes. However, Li transport in these systems is much less understood than for crystalline materials. We investigate amorphous LiPON electrolytes via ab initio molecular dynamics, providing atomistic-level insight into the mechanisms underlying the Li+ mobility. We find that the latter is strongly influenced by the chemistry and connectivity of phosphate polyanions near Li+. Amorphization generates edge-sharing polyhedral connections between Li­(O,N)4 and P­(O,N)4, and creates under- and overcoordinated Li sites, which destabilizes the Li+ and enhances their mobility. N substitution for O favors conductivity in two ways: (1) excess Li accompanying 1­(N):1­(O) substitutions introduces extra carriers; (2) energetically favored N-bridging substitutions condense phosphate units and densify the structure, which, counterintuitively, corresponds to higher Li+ mobility. Finally, bridging N is not only less electronegative than O but also engaged in strong covalent bonds with P. This weakens interactions with neighboring Li+ smoothing the way for their migration. When condensation of PO4 polyhedra leads to the formation of isolated O anions, the Li+ mobility is reduced, highlighting the importance of oxygen partial pressure control during synthesis. This detailed understanding of the structural mechanisms affecting Li+ mobility is the key for optimizing the conductivity of LiPON and other amorphous Li-ion conductors.

Lithium phosphorus oxynitride, also known as Lipon, solid-state electrolytes are at the center of the search for solid-state Li metal batteries. Key to the performance of Lipon is a combination of high Li content, amorphous character, and the incorporation of N into the structure. Despite the material's importance, our work presents the first study to fully resolve the structure of Lipon using a combination of  ab initio molecular dynamics, density functional theory, neutron scattering, and infrared spectroscopy. The modeled and experimental results have exceptional agreement in both neutron pair distribution function and infrared spectroscopy. Building on this synergy, the structural models show that N forms both bridges between two phosphate units and nonbridging apical N. We further show that as the Li content is increased the ratio of bridging to apical N shifts from being predominantly bridging at Li contents around 2.5:1 Li:P to only apical N at higher Li contents of 3.38:1 Li:P. This crossover from bridging to apical N appears to directly correlate with and explain both the increase in ionic conductivity with the incorporation of N and the ionic conductivity trends found in the literature.

Calculated voltage stability window of selected Na oxides.

CRYSTAL is a periodic ab initio code that uses a Gaussian-type basis set to express crystalline orbitals (i.e. Bloch functions). The use of atom-centred basis functions allows treating 3D (crystals), 2D (slabs), 1D (polymers) as well as 0D (molecules) systems on the same grounds. In turn, all-electron calculations are inherently permitted along with pseudopotential strategies. A variety of density functionals is implemented, including global and range-separated hybrids of various nature and, as an extreme case, Hartree-Fock (HF). The cost for HF or hybrids is only about 3-5 times larger than when using the local density approximation (LDA) or the generalized gradient approximation (GGA). Symmetry is fully exploited at all steps of the calculation. Many tools are available to modify the structure as given in input and simplify the construction of complicated objects, such as slabs, nanotubes, molecules, clusters. Many tensorial properties can be evaluated by using a single input keyword: elastic, piezoelectric, photoelastic, dielectric, as well as first and second hyperpolarizabilies, etc. The calculation of infrared and Raman spectra is available, and the intensities are computed analytically. Automated tools are available for the generation of the relevant configurations of solid solutions and/or disordered systems. Three versions of the code exist, serial, parallel and massive-parallel. In the second one the most relevant matrices are duplicated on each core, whereas in the third one the Fock matrix is distributed for diagonalization. All the relevant vectors are dynamically allocated and deallocated after use, making the code very agile. CRYSTAL can be used efficiently on high performance computing machines up to thousands of cores.

Titanium dioxide is one of the most important metal oxides because of its applications as a white pigment, as an important component in solar cells, and as a photocatalyst. 1 In the last two applications, the relevant phenomena are occurring at the surface of anatase nanoparticles, which are generally considered to be more active than rutile ones. 2 Therefore, it is relevant for both technological and fundamental motivations to study the structure of the different surfaces terminating the anatase nanocrystals. This study can be performed both experimentally and theoretically.Concerning the experimental approach, the use of Fourier transform infrared (FTIR) spectroscopy of adsorbed probe molecules has emerged as the leading method. 3 In particular, carbon monoxide, a weak Lewis base, is usually chosen to probe the Lewis acid sites of TiO 2 . 4À8 The stretching frequency of the adsorbed CO is related to the electrophilicity and polarizing power of the surface Lewis acid sites: the greater the electrophilicity of the metal cation, the higher the blue shift with respect to the value in the gas phase (2143 cm À1 ). 4 The variation of the stretching frequency originates from the combination of different mechanisms: (1) the interaction between the CO dipole moment and the surface electric field (Stark effect), (2) the repulsive potential due to the vibration of the CO molecule against a rigid surface (wall effect), and 9 (3) the dipoleÀdipole interactions between the adsorbed molecules. 10 However, when highly dispersed phases are concerned, the particles expose a variety of faces, and consequently, the IR spectra of adsorbed CO can be constituted by the superposition of several components whose unambiguous assignment is troublesome. For oxides characterized by a rock salt structure, such as MgO, a satisfactory interpretation of the spectra of adsorbed CO has been obtained by comparing the IR spectra with high-resolution transmission electron microscopy (HRTEM) results. 11 This has been made possible by the simple cubic morphology of the MgO particles, which definitely exposes a predominant family of faces, a fact which makes the interpretation of the HRTEM images straightforward. In the case of highsurface-area TiO 2 , the determination of the nanoparticles' morphology by HRTEM is much more difficult, and consequently, the combined use of electron microscopy and IR spectroscopy of adsorbed CO is not so fruitful. This is the case where the help of a computational study on the structure of the most probably exposed surfaces and on the vibrational properties of CO adlayers adsorbed on them can be of invaluable utility. This approach has dual importance: in fact, while on one side, it helps the interpretation of IR results, on the other side, it allows one to ABSTRACT: Periodic DFT calculations of the structure of (101), (100), (001), and (112) anatase faces and of the vibrational properties of CO adsorbed on them at two coverages allow assigning the main features of FTIR spectra of CO adsorbed at 60 K on highly dehydroxyl...

In this paper we develop the stability rules for NASICON-structured materials, as an example of compounds with complex bond topology and composition. By first-principles high-throughput computation of 3881 potential NASICON phases, we have developed guiding stability rules of NASICON and validated the ab initio predictive capability through the synthesis of six attempted materials, five of which were successful. A simple two-dimensional descriptor for predicting NASICON stability was extracted with sure independence screening and machine learned ranking, which classifies NASICON phases in terms of their synthetic accessibility. This machine-learned tolerance factor is based on the Na content, elemental radii and electronegativities, and the Madelung energy and can offer reasonable accuracy for separating stable and unstable NASICONs. This work will not only provide tools to understand the synthetic accessibility of NASICON-type materials, but also demonstrates an efficient paradigm for discovering new materials with complicated composition and atomic structure.

The key challenges in all-solid-state batteries (ASSBs) are establishing and maintaining perfect physical contact between rigid components for facile interfacial charge transfer, particularly between the solid electrolyte and cathode, during repeated electrochemical cycling. Here, we introduce inorganic-based pliable solid electrolytes that exhibit extraordinary clay-like mechanical properties (storage and loss moduli <1 MPa) at room temperature, high lithium-ion conductivity (3.6 mS cm −1 ), and a glass transition below −50°C. The unique mechanical features enabled the solid electrolyte to penetrate into the high-loading cathode like liquid, thereby providing complete ionic conduction paths for all cathode particles as well as maintaining the pathway even during cell operation. We propose a design principle in which the complex anion formation including Ga, F, and a different halogen can induce the claylike features. Our findings provide new opportunities in the search for solid electrolytes and suggest a new approach for resolving the issues caused by the solid electrolyte−cathode interface in ASSBs.

The computational scheme for the evaluation of the second-order electric susceptibility tensor in periodic systems, recently implemented in the CRYSTAL code within the coupled perturbed Hartree-Fock (HF) scheme, has been extended to local-density, gradient-corrected, and hybrid density functionals (coupled-perturbed Kohn-Sham) and applied to a set of cubic and hexagonal semiconductors. The method is based on the use of local basis sets and analytical calculation of derivatives. The high-frequency dielectric tensor (epsilon(infinity)) and second-harmonic generation susceptibility (d) have been calculated with hybrid functionals (PBE0 and B3LYP) and the HF approximation. Results are compared with the values of epsilon(infinity) and d obtained from previous plane-wave local density approximation or generalized gradient approximation calculations and from experiment. The agreement is in general good, although comparison with experiment is affected by a certain degree of uncertainty implicit in the experimental techniques.