Frenkel‐Defect‐Mediated Chemical Ordering Transition in a Li–Mn–Ni Spinel Oxide

Using spinel‐type Li(Mn_1.5Ni_0.5)O₄ with two different cations, Mn and Ni, in the oxygen octahedra as a model system, we show that a cation ordering transition takes place through the formation of Frenkel‐type point defects. A series of experimental results based on atomic‐scale observations and in situ powder diffractions along with ab initio calculations consistently support such defect‐mediated transition behavior. In addition to providing a precise suggestion of the intermediate transient states and the resulting kinetic pathway during the transition between two phases, our findings emphasize the significant role of point defects in ordering transformation of complex oxides.     

[{(CH3)3Si}3C–Li–C{Si(CH3)3}3][Li · 3(OC4H8)] und {(CH3)3Si}3C–Li · O=C(Si(CH3)3)2, zwei neue Addukte des Lithium‐trisylmethanids

[{(CH₃)₃Si}₃C–Li–C{Si(CH₃)₃}₃][Li · 3(OC₄H₈)] and {(CH₃)₃Si}₃C–Li · O=C(Si(CH₃)₃)₂, two New Adducts of Lithium Trisylmethanide Sublimation of (Tsi–Li) · 2 THF (Tsi = –C(Si(CH₃)₃)₃) at 180 °C and 10^–4 hPa gives (Tsi–Li) · 1.5 THF in very low yield. The X‐ray structure determination shows an almost linear [Tsi–Li–Tsi]^– anion connected by short agostic Li…C contacts with the threefold THF‐coordinated Li‐cation. Base‐free Tsi–Li, solved in toluene is decomposed by oxygen, forming the strawberry‐colored ketone O=C(SiMe₃)₂, which forms an 1 : 1 adduct with undecomposed Tsi–Li. The X‐ray structure elucidation of this compound is also discussed.     

Recycling Application of Li–MnO2 Batteries as Rechargeable Lithium–Air Batteries

The ever‐increasing consumption of a huge quantity of lithium batteries, for example, Li–MnO₂ cells, raises critical concern about their recycling. We demonstrate herein that decayed Li–MnO₂ cells can be further utilized as rechargeable lithium–air cells with admitted oxygen. We further investigated the effects of lithiated manganese dioxide on the electrocatalytic properties of oxygen‐reduction and oxygen‐evolution reactions (ORR/OER). The catalytic activity was found to be correlated with the composition of Li_xMnO₂ electrodes (0<x<1) generated in situ in aprotic Li–MnO₂ cells owing to tuning of the Mn valence and electronic structure. In particular, modestly lithiated Li_0.50MnO₂ exhibited superior performance with enhanced round‐trip efficiency (ca. 76 %), high cycling ability (190 cycles), and high discharge capacity (10 823 mA h g_carbon^?1). The results indicate that the use of depleted Li–MnO₂ batteries can be prolonged by their application as rechargeable lithium–air batteries.     

Spatial,Hysteretic, and Adaptive Host–Guest Chemistry in a Metal–Organic Framework with Open Watson–Crick Sites

Biological and artificial molecules and assemblies capable of supramolecular recognition, especially those with nucleobase pairing, usually rely on autonomous or collective binding to function. Advanced site‐specific recognition takes advantage of cooperative spatial effects, as in local folding in protein–DNA binding. Herein, we report a new nucleobase‐tagged metal–organic framework (MOF), namely ZnBTCA (BTC=benzene‐1,3,5‐tricarboxyl, A=adenine), in which the exposed Watson–Crick faces of adenine residues are immobilized periodically on the interior crystalline surface. Systematic control experiments demonstrated the cooperation of the open Watson–Crick sites and spatial effects within the nanopores, and thermodynamic and kinetic studies revealed a hysteretic host–guest interaction attributed to mild chemisorption. We further exploited this behavior for adenine–thymine binding within the constrained pores, and a globally adaptive response of the MOF host was observed.     

Molecular Double‐Bond Covalent Radii for Elements Li–E112

The previous systems of triple‐bond and single‐bond self‐consistent, additive covalent radii, R(AB)=r(A)+ r(B), are completed with a fit for σ²π² double‐bonds.The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same, self‐consistent fit. Many of the calculated primary data came from E?CH₂ and H? E?CH₂ models. Homonuclear LE?EL, formaldehyde‐type Group 14–Group 16 and open‐shell, X ³ Σ Group‐16 dimer data are included. The standard deviation for the 316 included data points is 3 pm.     

Understanding LiOH Chemistry in a Ruthenium‐Catalyzed Li–O2 Battery

Non‐aqueous Li–O₂ batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li₂O₂, have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru‐catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e⁻ oxygen reduction reaction, the H in LiOH coming solely from added H₂O and the O from both O₂ and H₂O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li₂O₂, LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long‐lived battery. An optimized metal‐catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals.     

Molecular dynamics simulation of ionic transport on molten Li–KCl interface

A molecular dynamics study is performed to determine the dynamics and transport properties of the ions on the molten interface between anode metal Li and electrolyte KCl. Radial distribution function of the ionic pair and the behavior of the mean‐square displacement (MSD) as a function of time (t) indicate that KCl and metal Li are in the molten state at 2,200 K in the canonical ensemble. The dynamics of the ionic transport are characterized by studying MSD for the centers of mass of the ions at different temperatures. Diffusion coefficient is evaluated from the linear slope of the MSD (t) function in the range of 0–500 ps. The MSD and diffusion coefficient of the Li⁺ ions are much larger than those of the Cl^? and K⁺ ions due to the difference in ionic characteristic. The transport process has been dominated by the Li⁺ ions on the molten interface and the Li⁺ ions are main charge carriers. The energy barrier of the Li⁺ ions transporting into the molten KCl is fitted to be 5.28 kcal/mol in the light of the activation model. The electrical conductivity of the Li⁺ ions transporting into the molten KCl are calculated from the Nernst–Einstein formula to be in the range of 0.2–0.3 S cm^?1. The current density resulted from the Li⁺ ions through the interface are estimated to be an order of 10⁶ A cm^?2, which may be the value corresponding to a larger concentration gradient of the Li⁺ ions. Simulated results at different temperatures show that the diffusion coefficient, conductivity and current density have increased with the temperature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A New Perspective on Li–SO2 Batteries for Rechargeable Systems

Primary Li–SO₂ batteries offer a high energy density in a wide operating temperature range with exceptionally long shelf life and have thus been frequently used in military and aerospace applications. Although these batteries have never been demonstrated as a rechargeable system, herein, we show that the reversible formation of Li₂S₂O₄, the major discharge product of Li–SO₂ battery, is possible with a remarkably smaller charging polarization than that of a Li–O₂ battery without the use of catalysts. The rechargeable Li–SO₂ battery can deliver approximately 5400 mAh g^?1 at 3.1 V, which is slightly higher than the performance of a Li–O₂ battery. In addition, the Li–SO₂ battery can be operated with the aid of a redox mediator, exhibiting an overall polarization of less than 0.3 V, which results in one of the highest energy efficiencies achieved for Li–gas battery systems.     

Specific heats of ternary oxides in the Li–U(VI)–O System

Seven ternary oxides; Li₄UO₅, Li₂UO₄, Li₂₂U₁₈O₆₅, Li₂U_1.75O_6.25, Li₂U₂O₇, Li₂U₃O₁₀ and Li₂U₆O₁₉ in the system Li–U(VI)–O were prepared by solid-state reaction route and characterized by X-ray diffraction method. Specific heats of these compounds were measured by differential scanning calorimetry in the temperature range from 300 to 860 K. The specific heats show a decreasing trend with increase in UO₃(s) content in these lithium uranates. However, the specific heat per gram atom shows an increasing trend with decrease in number of oxygen atoms in the formula unit.     

The First Introduction of Graphene to Rechargeable Li–CO2 Batteries

The utilization of the greenhouse gas CO₂ in energy‐storage systems is highly desirable. It is now shown that the introduction of graphene as a cathode material significantly improves the performance of Li–CO₂ batteries. Such batteries display a superior discharge capacity and enhanced cycle stability. Therefore, graphene can act as an efficient cathode in Li–CO₂ batteries, and it provides a novel approach for simultaneously capturing CO₂ and storing energy.     

Three Dimensionally Ordered Mesoporous Carbon as a Stable,High‐Performance Li–O2 Battery Cathode

Enabled by the reversible conversion between Li₂O₂ and O₂, Li–O₂ batteries promise theoretical gravimetric capacities significantly greater than Li‐ion batteries. The poor cycling performance, however, has greatly hindered the development of this technology. At the heart of the problem is the reactivity exhibited by the carbon cathode support under cell operation conditions. One strategy is to conceal the carbon surface from reactive intermediates. Herein, we show that long cyclability can be achieved on three dimensionally ordered mesoporous (3DOm) carbon by growing a thin layer of FeO_x using atomic layer deposition (ALD). 3DOm carbon distinguishes itself from other carbon materials with well‐defined pore structures, providing a unique material to gain insight into processes key to the operations of Li–O₂ batteries. When decorated with Pd nanoparticle catalysts, the new cathode exhibits a capacity greater than 6000 mAh g_carbon^?1 and cyclability of more than 68 cycles.     

Crystallization‐Driven Self‐Assembly of Rod–Coil–Rod Pseudopolyrotaxanes into Spherical Micelles,Nanorods, and Nanorings in Aqueous Solutions

A novel rod‐containing block copolymer is constructed by supramacromolecular self‐assembly of α‐cyclodextrin and a triblock copolymer with methoxy polyethylene glycol as the flanking chains and the midterm block alternately connected by 2,2‐dimethylolbutyric acid and isophorone diisocyanate. The assembled rod‐containing block copolymer shows an exciting phenomenon of concentration‐ and pH‐dependent morphological switching of well‐defined nanostructures. In the solutions at pH 9.2, spherical micelles, rod‐like micelles, and hydrogel are observed successively with an increase of the concentration. Notably, the rod‐like micelles are composed of spherical segments due to the combination of the crystalline cores of the spherical micelles. In addition, 1D nanostructures with different curvatures from linear rod‐like micelles (pH 9.2) to ring‐shaped micelles (pH 7.5) can be obtained by controlling the pH values of the assembled systems.