RESUMO
Metallothermic, especially magnesiothermic, solid-state reactions have been widely applied to synthesize various materials. However, further investigations regarding the use of this method for composite syntheses are needed because of the high reactivity of magnesium. Herein, we report an in situ magnesiothermic reduction to synthesize a composite of Ge@C as an anode material for lithium-ion batteries. The obtained electrode delivered a specific capacity of 454.2 mAh·g-1 after 200 cycles at a specific current of 1000 mA·g-1. The stable electrochemical performance and good rate performance of the electrode (432.3 mAh·g-1 at a specific current of 5000 mA·g-1) are attributed to the enhancement in distribution and chemical contact between Ge nanoparticles and the biomass-based carbon matrix. A comparison with other synthesis routes has been conducted to demonstrate the effectiveness of contact formation during in situ synthesis.
RESUMO
This study focuses on the effects of the chemical process and heating time at 900 °C on pristine anthracite coal (provided by Vang Danh coal, Quang Ninh province, Vietnam) and explores its structure and electrochemical performance when used as an anode in Na-ion batteries. After chemical treatment with NaOH and H2SO4, the impurity content in the raw material decreased significantly (e.g., ash content dropped from 4.4% to 0.9%, etc.). The interspacing between the graphene layers in the anthracite structure also increased after the heat treatment. Besides, on extending the heating time, the anthracite structure became more disordered than the samples heated for shorter times. Therefore, the intercalation ability of Na+ ions in the anthracite structure increased, and the sample heated at 900 °C for 6 hours exhibited the highest reversible capacity of up to 160 mA h g-1 with adequate capacity retention after 100 cycles at C/10 rate.
RESUMO
Magnesium batteries, like lithium-ion batteries, with higher abundance and similar efficiency, have drawn great interest for large-scale applications such as electric vehicles, grid energy storage and many more. On the other hand, the use of organic electrode materials allows high energy-performance, metal-free, environmentally friendly, versatile, lightweight, and economically efficient magnesium storage devices. In particular, the structural diversity and the simple activity of organic molecules make redox properties, and hence battery efficiency, easy to monitor. While organic magnesium batteries still in their infancy, this field becomes more and more promising because significant results were reported. To summarize the achievements in studies on organic cathodes for magnesium systems, their synthesis is discussed, combined with electrode design to provide the basis for controlling the electrochemical properties. Moreover, the techniques to synthesize organic materials with high-yield are mentioned. Finally, potential problems and prospects are explored to further improve organic cathodes.
RESUMO
Low-melting ionic liquid, IL, based on small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), where R(1), R(2), R(3) = CH(3) or C(2)H(5), R = C(3)H(7), C(4)H(9), C(6)H(13), C(8)H(17), CF(3)C(3)H(6)) and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs, including melting point, glass transition, and degradation temperatures; viscosity; density; ionic conductivity; diffusion coefficient; and electrochemical stability, were determined. Heteronuclear Overhauser NMR spectroscopy experiments were also performed to point out the presence of pair correlation between the different moieties. The LiTFSI addition effect on the IL properties was studied with the same methodology. Some nanoscale organization with segregation of polar and apolar domains was observed. ILs with small alkyl chain length or fluorinated ammonium exhibit very high electrochemical stability in oxidation.
