On the Origin of the Non-Arrhenius Na-ion Conductivity in Na3 OBr.

The sodium-rich antiperovskites (NaRAPs) with composition Na3 OB (B=Br, Cl, I, BH4 , etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na3 OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes.

Tracer diffusion coefficients of Li+ ions in c-axis oriented LixCoO2 thin films measured by secondary ion mass spectrometry.

Lithium diffusion is a key factor in determining the charge/discharge rate of Li-ion batteries. Herein, we study the tracer diffusion coefficient (D*) of lithium ions in the c-axis oriented LiCoO2 thin film using secondary ion mass spectrometry (SIMS). We applied a step-isotope-exchange method to determine D* in the Li-extracted LixCoO2. The observed values of D* ranged from 2 × 10-12 to 3 × 10-17 cm2 s-1 depending on the compositions in the range of 0.4 < x < 1.0. Approaching the stoichiometric composition (x = 1.0), D* decreases steeply to the minimum, which can be explained by the vacancy diffusion mechanism. Electrochemically determined diffusion coefficients corrected by thermodynamic factors are found to be in good agreement with D* determined by our method, over a wide range of compositions. The c-axis diffusion was explained by the migration of Li+ ions from one layer to another through additional diffusion channels, such as antiphase boundaries and a pair of Li antisite and oxygen vacancies in cobalt oxide layers.

Structural change of NaO1/2-WO3-NbO5/2-LaO3/2-PO5/2 glass induced by electrochemical substitution of sodium ions with protons.

Structural changes of 35NaO1/2-1WO3-8NbO5/2-5LaO3/2-51PO5/2 glass (1W-glass) before and after the electrochemical substitution of sodium ions with protons by alkali-proton substitution (APS) are studied by Raman and (31)P magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies. The glass before APS consists of (PO3(-))8.6(P2O7(4-)) chains on average and the terminal Q(1) units (-O-PO3(3-)) are bound to MO6 octahedra (M denotes niobium or tungsten) through P-O-M bonds. Some non-bridging oxygens (NBOs) in the MO6 octahedra are present in addition to the bridging oxygens (BOs) in P-O-M bonds. APS induces fragmentation of the phosphate chains because the average chain length decreases to (PO3(-))3.7(P2O7(4-)) after APS, despite the total number of modifier cations of sodium and lanthanum ions and protons being unaffected by APS. This fragmentation is induced by some of the NBOs in the MO6 octahedra before APS, changing to BOs of the newly formed M-O-P bonds after APS, because of the preferential formation of P-OH bonds over M-OH ones in the present glass. We show that APS under the conditions used here is not a simple substitution of sodium ions with protons, but it is accompanied by the structural relaxation of the glass to stabilize the injected protons.

Lithium ion diffusion in Li ß-alumina single crystals measured by pulsed field gradient NMR spectroscopy.

The lithium ion diffusion coefficient of a 93% Li ß-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10(-11) m(2)/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10(-13) m(2)/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the ß-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297-333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li ß-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li ß-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li ß-alumina system.

Understanding Ion Dynamics in Closoborate-Type Lithium-Ion Conductors on Different Time-Scales.

The lithium-ion transport mechanism in 0.7Li(CB9H10)-0.3Li(CB11H12) complex hydride solid electrolyte was studied over a wide time-scale (ns-ms) by choosing appropriate techniques for assessing ionic motion on the desired time-scale using nuclear magnetic resonance (NMR) relaxation, AC impedance, and pulsed field gradient-NMR (PFG-NMR) measurements. The 7Li NMR line width decreased with increasing temperature, and the spin-lattice relaxation time T1 for the cation and anions showed a minimum near 303 K, indicating that the lithium ions and the anions were highly mobile. The activation energy estimated from the analysis of the NMR relaxation time matched well with the values estimated from the AC impedance and PFG-NMR. This confirms that the lithium-ion motion in 0.7Li(CB9H10)-0.3Li(CB11H12) is the same over a wide time-scale, suggesting steady Li-ion motion over a wide transport range. This understanding offers insights into strategies for designing complex hydride lithium superionic conductors.

On the Origin of the Non-Arrhenius Na-ion Conductivity in Na3OBr.

The sodium-rich antiperovskites (NaRAPs) with composition Na3OB (B=Br, Cl, I, BH4, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na3OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes.

Fast fluoride ion conduction of NH4(Mg1-xLix)F3-x and (NH4)2(Mg1-xLix)F4-x assisted by molecular cations.

Aiming development of the fast anion conductors, we proposed a new material design using flexible molecular cation as a host cation, and demonstrated it with fluoride ion conduction in NH4MgF3 and (NH4)2MgF4 based materials. Dominant fluoride ion conduction with relatively high conductivities of 4.8 × 10-5 S cm-1 and 8.4 × 10-6 S cm-1 were achieved at 323 K in (NH4)2(Mg0.85Li0.15)F3.85 and NH4(Mg0.9Li0.1)F2.9, respectively. It is implied that the molecular cation in the host lattice can assist the anion conduction. Our findings suggest molecular cation-containing compounds can be attractive material groups for fast anion conductors.

A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries.

All-solid-state batteries incorporating lithium metal anode have the potential to address the energy density issues of conventional lithium-ion batteries that use flammable organic liquid electrolytes and low-capacity carbonaceous anodes. However, they suffer from high lithium ion transfer resistance, mainly due to the instability of the solid electrolytes against lithium metal, limiting their use in practical cells. Here, we report a complex hydride lithium superionic conductor, 0.7Li(CB9H10)-0.3Li(CB11H12), with excellent stability against lithium metal and a high conductivity of 6.7 × 10-3 S cm-1 at 25 °C. This complex hydride exhibits stable lithium plating/stripping reaction with negligible interfacial resistance (<1 Ω cm2) at 0.2 mA cm-2, enabling all-solid-state lithium-sulfur batteries with high energy density (>2500 Wh kg-1) at a high current density of 5016 mA g-1. The present study opens up an unexplored research area in the field of solid electrolyte materials, contributing to the development of high-energy-density batteries.

Electrochemically Synthesized Tin/Lithium Alloy To Convert Laser Light to Extreme Ultraviolet Light.

This paper describes lithium-tin alloys as a novel target material to enhance the efficiency of 13.5 nm extreme ultraviolet (EUV) light from generated laser-produced plasmas. Both lithium and tin exhibit EUV emission with the same peak at 13.5 nm. We show that lithium-tin (LiSn) alloys exhibit emission also at 13.5 nm and a mixture of tin and lithium emission by illuminating Nd:YAG laser (1 ns, 2.5 × 1010, 7.1 × 1010 W/cm2). The emission spectra and emission angular distribution by using phosphor imaging plates were analyzed to obtain the conversion efficiency from laser light to 13.5 nm light. The Li-Sn alloys were slightly higher than planar tin and between tin and lithium. It would be due to the suppression of self-absorption of 13.5 nm light by the tin plasma.