Ionic Liquid Electrolytes with Various Sodium Solutes for Rechargeable Na/NaFePO₄ Batteries Operated at Elevated Temperatures

NaFePO₄ with an olivine structure is synthesized via chemical delithiation of LiFePO₄ followed by electrochemical sodiation of FePO₄. Butylmethylpyrrolidinium–bis­(trifluoromethanesulfonyl)­imide (BMP–TFSI) ionic liquid (IL) with various sodium solutes, namely NaBF₄, NaClO₄, NaPF₆, and NaN­(CN)₂, is used as an electrolyte for rechargeable Na/NaFePO₄ cells. The IL electrolytes show high thermal stability (>350 °C) and nonflammability, and are thus ideal for high-safety applications. The highest conductivity and the lowest viscosity of the electrolyte are obtained with NaBF₄. At an elevated temperature (above 50 °C), the IL electrolyte is more suitable than a conventional organic electrolyte for the sodium cell. At 75 °C, the measured capacity of NaFePO₄ in a NaBF₄-incorporated IL electrolyte is as high as 152 mAh g^–1 (at 0.05 C), which is near the theoretical value (154 mAh g^–1). Moreover, 60% of this capacity can be retained when the charge–discharge rate is increased to 1 C

Combinatorial Studies on Wet-Chemical Synthesized Ti-Doped α‑Fe₂O₃: How Does Ti⁴⁺ Improve Photoelectrochemical Activity?

Hematite (α-Fe₂O₃)-based photoanode for photoelectrochemical water oxidation has been intensively studied for decades. Doping with isovalent or aliovalent ions is one way to mitigate several intrinsic drawbacks of bare hematite. While addition of Ti in the bulk has been reported for improving photoresponse, several aspects of effects of Ti impregnation have not been justified. In this work, Ti:Fe₂O₃ nanoellipsoids synthesized by a facile one-pot hydrothermal process present improved photoelectrochemical response. Tuned symmetry of Fe–O and Fe–Fe (Fe–Ti) with less recombination during charge transportation, tuned electron configuration of O_2p-Fe_4s4p hybridization in Ti-adjoining regime with enhanced electron relaxation within Fe₂O₃ lattice, suppressed O₂/H₂O back reaction (reduction of O₂), and inhibit formation of surface defects during hydrothermal synthesis were attested by X-ray absorption spectroscopy, Mott–Schottky analysis, and photoelectrochemical impedance spectroscopy. Additionally, Ti:Fe₂O₃ showed enhanced light absorption. Hydrogen evolution rate of 11.76 μmol h^–1 cm^–2 under illumination was observed while using Ti:Fe₂O₃ as the working electrode. Additional experiments on Mn⁴⁺ and In³⁺ incorporation showed mixed effects. This study provides insights and clarification toward “Ti-doping” of the hematite photoanode for solar hydrogen production from water

Scalable Patterning of MoS₂ Nanoribbons by Micromolding in Capillaries

In this study, we report a facile approach to prepare dense arrays of MoS₂ nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH₄)₂MoS₄) as the printing ink. The obtained MoS₂ nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS₂ nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10⁸ were achieved. The MoS₂ pattern can be printed on versatile substrates, such as SiO₂/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS₂ was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS₂ nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS₂. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoS_<i>x</i> structure (<i>x</i> ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoS_<i>x</i> was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm² and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS₂. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS₂/MoS_<i>x</i> nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials

Scalable Patterning of MoS₂ Nanoribbons by Micromolding in Capillaries

In this study, we report a facile approach to prepare dense arrays of MoS₂ nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH₄)₂MoS₄) as the printing ink. The obtained MoS₂ nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS₂ nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10⁸ were achieved. The MoS₂ pattern can be printed on versatile substrates, such as SiO₂/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS₂ was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS₂ nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS₂. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoS_<i>x</i> structure (<i>x</i> ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoS_<i>x</i> was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm² and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS₂. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS₂/MoS_<i>x</i> nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials

Electrolyte Optimization for Enhancing Electrochemical Performance of Antimony Sulfide/Graphene Anodes for Sodium-Ion Batteries–Carbonate-Based and Ionic Liquid Electrolytes

The electrolyte is a key component in determining the performance of sodium-ion batteries. A systematic study is conducted to optimize the electrolyte formulation for a Sb₂S₃/graphene anode, which is synthesized via a facile solvothermal method. The effects of solvent composition and fluoroethylene carbonate (FEC) additive on the electrochemical properties of the anode are examined. The propylene carbonate (PC)-based electrolyte with FEC can ensure the formation of a reliable solid-electrolyte interphase layer, resulting in superior charge–discharge performance, compared to that found in the ethylene carbonate (EC)/diethyl carbonate (DEC)-based electrolyte. At 60 °C, the carbonate-based electrolyte cannot function properly. At such an elevated temperature, however, the use of an <i>N</i>-propyl-<i>N</i>-methylpyrrolidinium bis­(fluorosulfonyl)­imide ionic liquid electrolyte is highly promising, enabling the Sb₂S₃/graphene electrode to deliver a high reversible capacity of 760 mAh g^–1 and retain 95% of its initial performance after 100 cycles. The present work demonstrates that the electrode sodiation/desodiation properties are dependent significantly on the electrolyte formulation, which should be optimized for various application demands and operating temperatures of batteries

Comparative Study on the Morphology-Dependent Performance of Various CuO Nanostructures as Anode Materials for Sodium-Ion Batteries

In this work, CuO samples with three different nanostructures, i.e., nanoflakes, nanoellipsoids, and nanorods, are successfully synthesized by a facile and environmentally friendly hydrothermal approach based on the use of different structure directing agents. The morphological influence on the anodic electrochemical performances, such as capacity, cycling stability, rate capability, and diffusion coefficient measurements of these different CuO nanostructures is comparatively investigated for sodium-ion batteries. The capacity and cycling stability are higher for the CuO nanorods (CuO-NRs) based electrode as compared to the cases of CuO nanoellipsoids (CuO-NEs) and CuO nanoflakes (CuO-NFs). At a low current density of 25 mA g^–1, the CuO-NRs based electrode exhibits an excellent reversible capacity of 600 mA h g^–1. It also exhibits a capacity of 206 mA h g^–1 after 150 cycles with a capacity retention of 73% even at a higher current density of 1000 mA g^–1. The exceptional performance of CuO-NRs is attributable to its slim nanorod morphology with a smaller particle size that provides a short diffusion path and the maximized surface area facilitating good diffusion in electrolytes, ensuring good electronic conductivity and cycling stability. The comparative analysis of these materials can provide valuable insights to design hierarchical nanostructures with distinct morphology to achieve better materials designed for sodium-ion batteries

Electrolyte Optimization for Enhancing Electrochemical Performance of Antimony Sulfide/Graphene Anodes for Sodium-Ion Batteries–Carbonate-Based and Ionic Liquid Electrolytes

The electrolyte is a key component in determining the performance of sodium-ion batteries. A systematic study is conducted to optimize the electrolyte formulation for a Sb₂S₃/graphene anode, which is synthesized via a facile solvothermal method. The effects of solvent composition and fluoroethylene carbonate (FEC) additive on the electrochemical properties of the anode are examined. The propylene carbonate (PC)-based electrolyte with FEC can ensure the formation of a reliable solid-electrolyte interphase layer, resulting in superior charge–discharge performance, compared to that found in the ethylene carbonate (EC)/diethyl carbonate (DEC)-based electrolyte. At 60 °C, the carbonate-based electrolyte cannot function properly. At such an elevated temperature, however, the use of an <i>N</i>-propyl-<i>N</i>-methylpyrrolidinium bis­(fluorosulfonyl)­imide ionic liquid electrolyte is highly promising, enabling the Sb₂S₃/graphene electrode to deliver a high reversible capacity of 760 mAh g^–1 and retain 95% of its initial performance after 100 cycles. The present work demonstrates that the electrode sodiation/desodiation properties are dependent significantly on the electrolyte formulation, which should be optimized for various application demands and operating temperatures of batteries

Influence of LiTFSI Addition on Conductivity, Diffusion Coefficient, Spin–Lattice Relaxation Times, and Chemical Shift of One-Dimensional NMR Spectroscopy in LiTFSI-Doped Dual-Functionalized Imidazolium-Based Ionic Liquids

An ionic liquid (IL) 1-allyl-3-(2-methoxyethyl)­imidazolium bis­(trifluoromethylsulfonyl)­imide ([AMO]­[TFSI]) is prepared, and the effect of the addition of LiTFSI into [AMO]­[TFSI] on the transport and physicochemical properties is studied herein. The diffusion coefficients of ¹H, ⁷Li, and ¹⁹F are determined using pulsed-gradient spin–echo NMR to study the dynamics of all ion species. The neat [AMO]­[TFSI] and LiTFSI-doped [AMO]­[TFSI] give approximately straight lines for the relationship of <i>D</i> vs <i>Tη</i>^–1, demonstrating that the Stokes–Einstein equation holds for the ionic diffusivity in the binary system. NMR <i>T</i>₁ relation time measurements show the ¹H-<i>T</i>₁ and ¹⁹F-<i>T</i>₁ of LiTFSI-doped [AMO]­[TFSI] decrease with the increase of Li salt concentration, which is due to the viscosity increases and the formation of stable coordination adducts of Li and TFSI when the salt concentration increases. From the study of chemical shift in one-dimensional NMR spectroscopy, an upfield shift in ¹H and ¹⁹F spectra is observed in ILs with increasing lithium salt concentration; the formation of ion clusters is the dominant effect after the addition of LiTFSI in [AMO]­[TFSI]