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Metal chalcogenides are promising candidates for various energy storage applications. Herein, a ternary Fe2GeS4 compound was synthesized using a simple solid-state method and applied as versatile electrodes for rechargeable Li/Na–Fe2GeS4 battery cathodes and Li/Na-ion battery anodes. In addition, distinctive Li and Na reaction pathways for Fe2GeS4 consisting of insertion and conversion reactions have been demonstrated. For its application as rechargeable Li/Na–Fe2GeS4 battery cathodes, Li‖Fe2GeS4 and Na‖Fe2GeS4 battery systems were electrochemically evaluated by controlling the cut-off voltages within the insertion reaction and they showed high electrochemical performance with high reversible volumetric capacities and cyclability with appropriate cell potentials (Li‖Fe2GeS4: ∼550 mA h cm−3 over 100 cycles with ∼1.6 V; Na‖Fe2GeS4: ∼555 mA h cm−3 over 100 cycles with ∼1.2 V). In addition, for using Fe2GeS4 as an anode for Li-ion batteries (LIBs) and Na-ion batteries (NIBs), graphene-wrapped Fe2GeS4 nanocomposite (Fe2GeS4-rGO) comprising Fe2GeS4 nanocrystallites (∼10–15 nm) embedded on reduced graphene oxide (rGO) was synthesized through a simple two-step synthetic method to improve the electronic/ionic conductivity, structural stability, and mechanical strain relaxation. The electrochemical test results indicated that the Fe2GeS4-rGO exhibited high initial reversible gravimetric capacities (730 mA h g−1 for LIB, 563 mA h g−1 for NIB), high rate capability (520 mA h g−1 at 3C for LIB, 470 mA h g−1 at 2C for NIB), and an excellent cycling performance at a high 1C rate (capacity retention: ∼100% over 500 cycles for LIBs, ∼93% over 200 cycles for NIBs). Therefore, we believe that Fe2GeS4 is a highly applicable compound material for various battery systems. [ABSTRACT FROM AUTHOR]

The development of high-capacity and high-power lithium-ion batteries (LIBs) is a key challenge to meet the increasing demand for advanced mobile electronics and electric vehicles. A novel high-capacity and high-power Ga2Te3 anode material for LIBs, which exhibits a distinctive reaction mechanism with Li ions, has been introduced in this study. Two types of Ga2Te3/C composite were prepared via different synthetic routes, namely carbon thermal decomposition (TD) and high-energy ball milling (BM), to improve the electrochemical performance of Ga2Te3 anodes, and their electrochemical performances were compared. The electrochemical evaluation results indicate that the Ga2Te3/C composite produced by BM (BM-Ga2Te3/C) showed better electrochemical performance by delivering much smaller Ga2Te3 nanocrystallites than the Ga2Te3/C composite produced by TD (TD-Ga2Te3/C). Furthermore, the BM-Ga2Te3/C anode showed a highly reversible initial volumetric capacity (1245 mA h cm−3), stable capacity retention (93.2% after 500 cycles), and excellent high-rate performance (∼1000 mA h cm−3 at 1C after 500 cycles). These high electrochemical performances, which were demonstrated via ex situ analyses, were attained by a unique three-step nano-confinement process of Ga2Te3 in BM-Ga2Te3/C. Thus, this study provides a new material development strategy of employing mechano- and electro-chemical nano-confinement processes to develop high-performance anodes for LIBs. [ABSTRACT FROM AUTHOR]

The capture, sequestration and utilization of carbon dioxide have attracted global attention in the environmental field, science and industry. The concurrent conversion of CO2 and CH4 is a reasonable solution to reduce greenhouse gases, but it remains a challenging research topic. Herein, we reveal the catalytic activity of bifunctional half-sandwich complexes (metal = Ru, Rh, and Ir) in the direct conversion of methane and carbon dioxide to acetic acid (AA) using density functional theory. The use of Ru/Rh/Ir metals with ethanediphosphine (PP), N-tosylethylenediamine (NNTs), and ethylene glycol (OO) ligands shows superb performance in lowering the free energy (ΔG) barrier (ΔG‡) for the conversion. To activate CH4 and CO2 molecules, we used extra additives to reduce the high energy barriers required by simple metal–ligand complexes. For CH4 activation, additives of AA and trifluoroacetic acid (TFA) were used to assist the proton abstraction in the Ru–NNTs/OO complexes, while no acid additives were used for the PP ligands. In the case of the PP ligands, the C–H activation occurs through a "concerted oxidative addition–reductive elimination" (OA–RE) process, whereas in the NNTs/OO ligands, C–H activation occurs through "cyclometallation deprotonation" (CMD) irrespective of the presence of acid additives. The reduction in ΔG‡ for CH4 activation in Ru–NNTs/OO is 5–10 kcal mol−1 using acid additives. In contrast, in Ru–PP, this ΔG‡ barrier is 20 kcal mol−1 without additives. For CO2 activation, AlCl3 (Lewis acid) was used to insert CO2 into the metal site of the Ru–NNTs/OO and Ru/Rh/Ir–PP complexes. The reduction in ΔG‡ using AlCl3 for CO2 activation in Ru–NNTs·AA/OO·2TFA and Ru/Rh/Ir–PP is 15–30 kcal mol−1. Then, the overall activation barrier is reduced to 20–27 kcal mol−1. [ABSTRACT FROM AUTHOR]

Here, we report, for the first time, the preparation of Sb2Te3 and the Sb2Te3/C nanocomposite by a simple solid-state synthetic route and their application as Li-ion battery anode materials. The nanocomposite showed an interesting reaction mechanism and outstanding electrochemical performance. [ABSTRACT FROM AUTHOR]

Zinc telluride (ZnTe) and a nanostructured ZnTe/C composite were prepared by a simple solid-state synthetic route, and their potential as electrode materials for rechargeable Li-ion batteries was investigated. The electrochemical conversion/partial recombination reactions between ZnTe and Li were determined using ex situ X-ray diffraction and extended X-ray absorption fine structure analysis. X-ray diffraction and high-resolution transmission electron microscopy confirmed that the ZnTe/C nanocomposite consisted of ZnTe nanocrystallites that were uniformly distributed within an amorphous carbon matrix. The nanostructured ZnTe/C composite electrode exhibited excellent electrochemical properties with a high capacity (1st charge: 530 mA h g−1), cycling durability (over 200 cycles), and fast rate capability (1 C: ca. 550 mA h g−1, 3 C: ca. 504 mA h g−1). [ABSTRACT FROM AUTHOR]

Co-Sb intermetallic compounds (CoSb, CoSb2, and CoSb3) were simply synthesized by solid-state synthesis routes and their potential as anode materials for Li-ion batteries was investigated. The CoSb3 electrode showed poor electrochemical behavior, but the CoSb and CoSb2 electrodes showed relatively good electrochemical performance. Additionally, the reaction mechanisms of CoSb, CoSb2, and CoSb3 with Li were identified using ex situ X-ray diffraction. To improve the electrochemical performance of the Co-Sb intermetallic compounds, nanostructured composites of these compounds modified with carbon were prepared using a high-energy mechanical milling technique. Among the fabricated nanocomposites, the CoSb2/C nanocomposite electrode comprising disproportionated nanocrystalline CoSb, amorphous Sb, and an amorphous carbon matrix showed excellent electrochemical properties, such as a high energy density (1st charge: 578 mA h g-1, or ~2895 mA h cm-3), cycling durability over 100 cycles (above 490 mA h g-1, or ~2450 mA h cm-3), high initial Coulombic efficiency (~78.1%), and a fast rate capability (1 C: 472 mA h g-1, 3 C: 415 mA h g-1). These excellent electrochemical properties demonstrated by the CoSb2/C nanocomposite electrode confirm its potential as an alternative anode material for Li-ion batteries. [ABSTRACT FROM AUTHOR]

A simple, inexpensive, fast, and scalable method of transforming micron-sized metal oxides into new intermetallic compound nanocomposites by a hybrid mechanochemical synthesis using a high-energy mechanical milling technique was developed. The SnSb/MOx (M = Al or Mg)/C nanocomposites, synthesized by the mechanochemical reduction of SnO and Sb2O3 with Al or Mg, respectively, in the presence of carbon, were confirmed, by using various analytical techniques, to be composed of extremely small SnSb nanocrystallites, amorphous Al2O3 or nanocrystalline MgO, and amorphous carbon. Among the fabricated nanocomposites, the SnSb/MgO/C nanocomposite showed excellent electrochemical properties, such as a high energy density (1st charge: 572 mA h g−1 or ca. 3800 mA h cm−3), cycling durability (above 490 mA h g−1 or ca. 3300 mA h cm−3 over 150 cycles), good initial coulombic efficiency (ca. 81.3%), and a fast rate capability (1C: 480 mA h g−1, 3C: 420 mA h g−1). These excellent electrochemical properties demonstrated by the SnSb-based nanocomposite electrodes confirmed their potential as alternative anode materials for Li-ion batteries. [ABSTRACT FROM AUTHOR]