Cubic Crystal-Structured SnTe for Superior Li- and Na-Ion Battery Anodes

A cubic crystal-structured Sn-based compound, SnTe, was easily synthesized using a solid-state synthetic process to produce a better rechargeable battery, and its possible application as a Sn-based high-capacity anode material for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was investigated. The electrochemically driven phase change mechanisms of the SnTe electrodes during Li and Na insertion/extraction were thoroughly examined utilizing various <i>ex situ</i> analytical techniques. During Li insertion, SnTe was converted to Li_4.25Sn and Li₂Te; meanwhile, during Na insertion, SnTe experienced a sequential topotactic transition to Na_<i>x</i>SnTe (<i>x</i> ≤ 1.5) and conversion to Na_3.75Sn and Na₂Te, which recombined into the original SnTe phase after full Li and Na extraction. The distinctive phase change mechanisms provided remarkable electrochemical Li- and Na-ion storage performances, such as large reversible capacities with high Coulombic efficiencies and stable cyclabilities with fast C-rate characteristics, by preparing amorphous-C-decorated nanostructured SnTe-based composites. Therefore, SnTe, with its interesting phase change mechanisms, will be a promising alternative for the oncoming generation of anode materials for LIBs and NIBs

Tin Selenides with Layered Crystal Structures for Li-Ion Batteries: Interesting Phase Change Mechanisms and Outstanding Electrochemical Behaviors

Tin selenides with layered crystal structures, SnSe and SnSe₂, were synthesized by a solid-state method and electrochemically tested for use as Li-ion battery anodes. The phase change mechanisms of these compounds were thoroughly evaluated by ex situ X-ray diffraction and Se K-edge extended X-ray absorption fine structure techniques. SnSe showed better electrochemical reversibility of Li insertion/extraction than SnSe₂, which was attributed to remarkable conversion/recombination reactions of the former compound during lithiation/delithiation. Additionally, the electrochemical performance of SnSe was further enhanced by preparing carbon-modified nanocomposites using two different methods, that is, heat treatment (HT) for producing a carbon coating using polyvinyl chloride as a precursor and high-energy ball milling (BM) using carbon black powder. The SnSe/C electrode produced by BM showed a highly reversible initial capacity of 726 mA h g^–1 with a good initial Coulombic efficiency of ∼82%, excellent cycling behavior (626 mA h g^–1 after 200 cycles), and a fast C-rate performance (580 mA h g^–1 at 2C rate)

Transition-Metal-Free Synthesis of Substituted Pyridines via Ring Expansion of 2‑Allyl‑2<i>H-</i>azirines

A new strategy to open the 2-allyl-2<i>H</i>-azirines by 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) promotion in metal-free conditions affording 1-azatrienes that <i>in situ</i> electrocyclize to the pyridines in good to excellent yields is reported. The reaction displays a broad substrate scope and good tolerance to a variety of substituents including aryl, alkyl, and heterocyclic groups. In addition, one-pot synthesis of pyridines from oximes via <i>in situ</i> formation of 2<i>H</i>-azirines was achieved

Expedient Synthesis of Highly Substituted Pyrroles via Tandem Rearrangement of α-Diazo Oxime Ethers

An efficient rhodium-catalyzed synthesis of 2<i>H</i>-azirines and pyrroles has been developed. Novel rearrangement of α-oximino ketenes derived from α-diazo oxime ethers provides 2<i>H</i>-azirines bearing quaternary centers and allows for subsequent rearrangement to highly substituted pyrroles in excellent yields

Highly Reversible and Superior Li-Storage Characteristics of Layered GeS₂ and Its Amorphous Composites

A layered GeS₂ material was assessed as an electrode material in the fabrication of superior rechargeable Li-ion batteries. The electrochemical Li insertion/extraction behavior of the GeS₂ electrode was investigated from extended X-ray absorption measurements as well as by cyclic voltammetry and differential capacity plots to better understand its Li insertion/extraction behavior. Using the Li insertion/extraction reaction mechanism of the GeS₂ electrode, an interesting amorphous GeS₂-based composite was developed and tested for use as a high-performance electrode. Interestingly, the amorphous GeS₂-based composite electrode exhibited highly reversible discharging and charging reactions, which were attributed to a conversion/recombination reaction. The amorphous GeS₂-based composite electrode exhibited highly reversible and outstanding electrochemical performances, a highly reversible capacity (first charge capacity: 1298 mAh g^–1) with a high first Coulombic efficiency (83.3%), rapid rate capability (ca. 800 mAh g^–1 at a high current rate of 700 mA g^–1), and long capacity retention over 180 cycles with high capacity (1100 mAh g^–1) thanks to its interesting electrochemical reaction mechanism. Overall, this layered GeS₂ and its amorphous GeS₂/C composite are novel alternative anode materials for the potential mass production of rechargeable Li-ion batteries with excellent performance

Sn-Based Nanocomposite for Li-Ion Battery Anode with High Energy Density, Rate Capability, and Reversibility

To design an easily manufactured, large energy density, highly reversible, and fast rate-capable Li-ion battery (LIB) anode, Co–Sn intermetallics (CoSn₂, CoSn, and Co₃Sn₂) were synthesized, and their potential as anode materials for LIBs was investigated. Based on their electrochemical performances, CoSn₂ was selected, and its C-modified nanocomposite (CoSn₂/C) as well as Ti- and C-modified nanocomposite (CoSn₂/<i>a</i>-TiC/C) was straightforwardly prepared. Interestingly, the CoSn₂, CoSn₂/C, and CoSn₂/<i>a</i>-TiC/C showed conversion/nonrecombination, conversion/partial recombination, and conversion/full recombination during Li insertion/extraction, respectively, which were thoroughly investigated using <i>ex situ</i> X-ray diffraction and extended X-ray absorption fine structure analyses. As a result of the interesting conversion/full recombination mechanism, the easily manufactured CoSn₂/<i>a</i>-TiC/C nanocomposite for the Sn-based Li-ion battery anode showed large energy density (first reversible capacity of 1399 mAh cm^–3), high reversibility (first Coulombic efficiency of 83.2%), long cycling behavior (100% capacity retention after 180 cycles), and fast rate capability (appoximately 1110 mAh cm^–3 at 3<i>C</i> rate). In addition, degradation/enhancement mechanisms for high-capacity and high-performance Li-alloy-based anode materials for next-generation LIBs were also suggested

Silicon Diphosphide: A Si-Based Three-Dimensional Crystalline Framework as a High-Performance Li-Ion Battery Anode

The development of an electrode material for rechargeable Li-ion batteries (LIBs) and the understanding of its reaction mechanism play key roles in enhancing the electrochemical characteristics of LIBs for use in various portable electronics and electric vehicles. Here, we report a three-dimensional (3D) crystalline-framework-structured silicon diphosphide (SiP₂) and its interesting electrochemical behaviors for superior LIBs. During Li insertion in the SiP₂, a three-step electrochemical reaction mechanism, sequentially comprised of a topotactic transition (0.55–2 V), an amorphization (0.25–2 V), and a conversion (0–2 V), was thoroughly analyzed. On the basis of the three-step electrochemical reaction mechanism, excellent electrochemical properties, such as high initial capacities, high initial Coulombic efficiencies, stable cycle behaviors, and fast-rate capabilities, were attained from the preparation of a nanostructured SiP₂/C composite. This 3D crystalline-framework-structured SiP₂ compound will be a promising alternative anode material in the realization and mass production of excellent, rechargeable LIBs