Structural and electrical properties of ceramic Li-ion conductors based on Li1.3_{1.3}Al0.3_{0.3}Ti1.7_{1.7}(PO4_4)3_3-LiF

The work presents the investigations of Li1.3Al0.3Ti1.7(PO4)3-xLiF Li-ion conducting ceramics with 0 < x < 0.3 by means of X-ray diffractometry (XRD), 7Li, 19F, 27Al and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density method. It has been shown that the total ionic conductivity of both as-prepared and ceramic Li1.3Al0.3Ti1.7(PO4)3 is low due to a grain boundary phase exhibiting high electrical resistance. This phase consists mainly of berlinite crystalline phase as well as some amorphous phase containing Al3+ ions. The electrically resistant phases of the grain boundary decompose during sintering with LiF additive. The processes leading to microstructure changes and their effect on the ionic properties of the materials are discussed in the frame of the brick layer model (BLM). The highest total ionic conductivity at room temperature was measured for LATP-0.1LiF ceramic sintered at 800{\deg}C and was equal to {\sigma}tot = 1.1 x 10-4 Scm-1

Impact of Li2.9_{2.9}B0.9_{0.9}S0.1_{0.1}O3.1_{3.1} glass additive on the structure and electrical properties of the LATP-based ceramics

The existing solid electrolytes for lithium ion batteries suffer from low total ionic conductivity, which restricts its usefulness for the lithium-ion battery technology. Among them, the NASICON-based materials, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP) exhibit low total ionic conductivity due to highly resistant grain boundary phase. One of the possible approaches to efficiently enhance their total ionic conductivity is the formation of a composite material. Herein, the Li2.9B0.9S0.1O3.1 glass, called LBSO hereafter, was chosen as an additive material to improve the ionic properties of the ceramic Li1.3Al0.3Ti1.7(PO4)3 base material. The properties of this Li1.3Al0.3Ti1.7(PO4)3-xLi2.9B0.9S0.1O3.1 (0 < x < 0.3) system have been studied by means of high temperature X-ray diffractometry (HTXRD), 7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. We show here that the introduction of the foreign LBSO phase enhances their electric properties. This study reveals several interesting correlations between the apparent density, the microstructure, the composition, the sintering temperature and the ionic conductivity. Moreover, the electrical properties of the composites will be discussed in the terms of the brick-layer model (BLM). The highest value of {\sigma}tot = 1.5 x 10-4 Scm-1 has been obtained for LATP-0.1LBSO material sintered at 800{\deg}C

Properties of LiMnBO3 glasses and nanostructured glass-ceramics

Polycrystalline LiMnBO3 is a promising cathode material for Li-ion batteries. In this work, we investigated the thermal, structural and electrical properties of glassy and nanocrystallized materials having the same chemical composition. The original glass was obtained via a standard meltquenching method. SEM and 7Li solid-state NMR indicate that it contains a mixture of two distinct glassy phases. The results suggest that the electrical conductivity of the glass is dominated by the ionic one. The dc conductivity of initial glass was estimated to be in the order of 10-18 S.cm-1 at room temperature. The thermal nanocrystallization of the glass produces a nanostructured glass-ceramics containing MnBO3 and LiMnBO3 phases. The electric conductivity of this glass-ceramics is increased by 6 orders of magnitude, compared to the starting material at room temperature. Compared to other manganese and borate containing glasses reported in the literature, the conductivity of the nanostructured glass ceramics is higher than that of the previously reported glassy materials. Such improved conductivity stems from the facilitated electronic transport along the grain boundaries

The D-HMQC MAS-NMR technique: An efficient tool for the editing of through-space correlation spectra between quadrupolar and spin-1/2 (³¹P, ²⁹Si, ¹H, ¹³C) nuclei

The D-HMQC (dipolar heteronuclear multiple-quantum coherence) technique is a recently developed NMR pulse sequence particularly suitable for the investigation of spatial proximity between quadrupolar and spin-1/2 nuclei. Compared to the cross-polarisation magic-angle spinning technique applied to a quadrupolar nucleus, D-HMQC does not require time-consuming optimisations and exhibits on the quadrupolar spin a better robustness to irradiation offset and to Cq values and radiofrequency field. Furthermore, the high robustness to irradiation offset makes of the D-HMQC sequence the technique of choice for the structural characterisation of materials especially at high magnetic field. We show here how the D-HMQC can be easily implemented and optimised to give access to the structural analysis of silicate-, phosphate-, carbon- and proton-containing materials. An emphasis will be on describing the most popular dipolar recoupling schemes that can be used in that sequence and providing their advantages and drawbacks

Observation of proximities between spin-1/2 and quadrupolar nuclei: Which heteronuclear dipolar recoupling method is preferable?

International audienc

Solvent-free high-field dynamic nuclear polarization of mesoporous silica functionalized with TEMPO

We report high-field magic-angle spinning dynamic nuclear polarization (MAS DNP) of mesoporous silica functionalized with nitroxide radicals. These results demonstrate that co-condensation can be employed to incorporate DNP polarizing agents into inorganic materials and that solvent-free DNP is feasible for porous materials. For the investigated material, the direct MAS DNP enhances the 29Si nuclear magnetic resonance (NMR) spectra, whereas the indirect MAS DNP via protons is inapplicable owing to the inefficiency of 1H → 29Si cross polarization transfer. Furthermore, the 29Si signals in direct experiments build up in a few seconds at 100 K. This fast polarization buildup improves the NMR sensitivity and will be useful for the investigation of direct DNP below 100 K

Double-quantum 19F-19F dipolar recoupling at ultra-fast magic angle spinning NMR: Apllication to the assignment of 19F spectra of inorganic fluorides

International audienc