Sparse Cyclic Excitations Explain the Low Ionic Conductivity of Stoichiometric Li₇La₃Zr₂O₁₂

We have performed long time-scale molecular dynamics simulations of the cubic and tetragonal phases of the solid lithium-ion-electrolyte Li7La3Zr2O12 (LLZO), using a first-principles param- eterised interatomic potential. Collective lithium transport was analysed by identifying dynamical excitations; persistent ion displacements over distances comparable to the separation between lithium sites, and string-like clusters of ions that undergo cooperative motion. We find that dynamical excitations in c-LLZO are frequent, with participating lithium numbers following an exponential distribution, mirroring the dynamics of fragile glasses. In contrast, excitations in t-LLZO are both temporally and spatially sparse, consisting preferentially of highly concerted lithium motion around closed loops. This qualitative difference is explained as a consequence of lithium ordering in t-LLZO, and provides a mechanistic basis for the much lower ionic conductivity of t-LLZO compared to c-LLZO

Synthesis, electrochemistry and First Principles Calculation studies of layered Li-Ni-Ti-O compounds

New layered cathode materials, Li₀.₉Ni₀.₄₅Ti₀.₅₅O₂, were synthesized by means of ion-exchange from Na₀.₉Ni₀.₄₅Ti₀.₅₅O₂. The degree of cation disordering in the material depends critically on the synthesis conditions. Longer times and higher temperatures in the ion-exchange process induced more cation disordering. However, the partially disordered phase showed better capacity retention than the least disordered phase. First principles calculations indicated this could be attributed to the migration of Ti⁺⁴ into the Li layer during the electrochemical testing, which seems to depend sensitively on the Ni⁺² -Ti⁺⁴ configuration in the transition metal layer. The poor conductivity of this material could also be the reason for its low specific capacity according to the Density of States (DOS) obtained from first principles calculations indicating that only Ni participates in the electronic conductivity.Singapore-MIT Alliance (SMA

Postnatal Tshz3 Deletion Drives Altered Corticostriatal Function and Autism Spectrum Disorder–like Behavior

International audienceBACKGROUND: Heterozygous deletion of the TSHZ3 gene, encoding for the teashirt zinc-finger homeobox family member 3 (TSHZ3) transcription factor that is highly expressed in cortical projection neurons (CPNs), has been linked to an autism spectrum disorder (ASD) syndrome. Similarly, mice with Tshz3 haploinsufficiency show ASD-like behavior, paralleled by molecular changes in CPNs and corticostriatal synaptic dysfunctions. Here, we aimed at gaining more insight into "when" and "where" TSHZ3 is required for the proper development of the brain, and its deficiency crucial for developing this ASD syndrome. METHODS: We generated and characterized a novel mouse model of conditional Tshz3 deletion, obtained by crossing Tshz3 flox/flox with CaMKIIalpha-Cre mice, in which Tshz3 is deleted in CPNs from postnatal day 2 to 3 onward. We characterized these mice by a multilevel approach combining genetics, cell biology, electrophysiology, behavioral testing, and bioinformatics. RESULTS: These conditional Tshz3 knockout mice exhibit altered cortical expression of more than 1000 genes, w50% of which have their human orthologue involved in ASD, in particular genes encoding for glutamatergic syn-apse components. Consistently, we detected electrophysiological and synaptic changes in CPNs and impaired corticostriatal transmission and plasticity. Furthermore, these mice showed strong ASD-like behavioral deficits. CONCLUSIONS: Our study reveals a crucial postnatal role of TSHZ3 in the development and functioning of the corticostriatal circuitry and provides evidence that dysfunction in these circuits might be determinant for ASD pathogenesis. Our conditional Tshz3 knockout mouse constitutes a novel ASD model, opening the possibility for an early postnatal therapeutic window for the syndrome linked to TSHZ3 haploinsufficiency

Revealing defects in crystalline lithium-ion battery electrodes by solid state NMR: applications to LiVPO4F

International audienceIdentifying and characterizing defects in crystalline solids is a challenging problem, particularly for lithium-ion intercalation materials, which often exhibit multiple stable oxidation and spin states as well as local ordering of lithium and charges. Here, we reveal the existence of characteristic lithium defect environments in the crystalline lithium-ion battery electrode LiVPO4F and establish the relative subnanometer-scale proximities between them. Well-crystallized LiVPO4F samples were synthesized with the expected tavorite-like structure, as established by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) measurements. Solid-state 7Li nuclear magnetic resonance (NMR) spectra reveal unexpected paramagnetic 7Li environments that can account for up to 20% of the total lithium content. Multidimensional and site-selective solid-state 7Li NMR experiments using finite-pulse radio frequency-driven recoupling (fp-RFDR) establish unambiguously that the unexpected lithium environments are associated with defects within the LiVPO4F crystal structure, revealing the existence of dipole–dipole-coupled defect pairs. The lithium defects exhibit local electronic environments that are distinct from lithium ions in the crystallographic LiVPO4F site, which result from altered oxidation and/or spin states of nearby paramagnetic vanadium atoms. The results provide a general strategy for identifying and characterizing lithium defect environments in crystalline solids, including paramagnetic materials with short 7Li NMR relaxation times on the order of milliseconds