Atomic-scale investigation of MgO growth on fused quartz using angle-dependent NEXAFS measurements

Reversible Magnesium Metal Cycling in Additive-Free Simple Salt Electrolytes Enabled by Spontaneous Chemical Activation

Rechargeable magnesium (Mg) batteries can offer higher volumetric energy densities and be safer than their conventional counterparts, lithium-ion batteries. However, their practical implementation is impeded due to the passivation of the Mg metal anode or the severe corrosion of the cell parts in conventional electrolyte systems. Here, we present a chemical activation strategy to facilitate the Mg deposition/stripping process in additive-free simple salt electrolytes. By exploiting the simple immersion-triggered spontaneous chemical reaction between reactive organic halides and Mg metal, the activated Mg anode exhibited an overpotential below 0.2 V and a Coulombic efficiency as high as 99.5% in a Mg(TFSI)₂ electrolyte. Comprehensive analyses reveal simultaneous evolution of morphology and interphasial chemistry during the activation process, through which stable Mg cycling over 990 cycles was attained. Our activation strategy enabled the efficient cycling of Mg full-cell candidates using commercially available electrolytes, thereby offering possibilities of building practical Mg batteries.

Deposition of Sol-Gel ZnO:Mg Films and Investigation of Their Structural and Optical Properties

This work presents a facile sol-gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 and 3 wt%) and post-annealing treatments (300-600 °C) on the film's structural, vibrational and optical properties is investigated. Undoped ZnO films crystallize in the wurtzite phase, with crystallite sizes ranging from 9.1 nm (300 °C) to 29.7 nm (600 °C). Mg doping deteriorates the film crystallization and shifting of 002 peak towards higher diffraction angles is observed, indicating the successful incorporation of Mg into the ZnO matrix. ZnO:Mg films (2 wt%) possess the smallest crystallite size, ranging from 6.2 nm (300 °C) to 25.2 nm (600 °C). The highest Mg concentration (3 wt%) results into a segregation of the MgO phase. Lattice constants, texture coefficients and Zn-O bond lengths are discussed. The diminution of the c lattice parameter is related to the replacement of Zn²⁺ by Mg²⁺ in the ZnO host lattice. The vibrational properties are studied by Fourier transform infrared (FTIR) spectroscopy. IR lines related to Mg-O bonds are found for ZnO:Mg films with dopant concentrations of 2 and 3 wt%. The optical characterization showed that the transmittance of ZnO:Mg thin films increased from 74.5% (undoped ZnO) to about 89.1% and the optical band gap energy from 3.24 to 3.56 eV. Mg doping leads to a higher refractive index compared to undoped ZnO films. The FESEM (field emission scanning electron microscopy) technique is used for observation of the surface morphology modification of ZnO:Mg films. The doped ZnO films possess a smoother grained surface structure, opposite to the wrinkle-type morphology of undoped sol-gel ZnO films. The smoother surface leads to improved transparency of ZnO:Mg films.

Synchrotron radiation based X-ray techniques for analysis of cathodes in Li rechargeable batteries

Li-ion rechargeable batteries are promising systems for large-scale energy storage solutions. Understanding the electrochemical process in the cathodes of these batteries using suitable techniques is one of the crucial steps for developing them as next-generation energy storage devices. Due to the broad energy range, synchrotron X-ray techniques provide a better option for characterizing the cathodes compared to the conventional laboratory-scale characterization instruments. This work gives an overview of various synchrotron radiation techniques for analyzing cathodes of Li-rechargeable batteries by depicting instrumental details of X-ray diffraction, X-ray absorption spectroscopy, X-ray imaging, and X-ray near-edge fine structure-imaging. Analysis and simulation procedures to get appropriate information of structural order, local electronic/atomic structure, chemical phase mapping and pores in cathodes are discussed by taking examples of various cathode materials. Applications of these synchrotron techniques are also explored to investigate oxidation state, metal-oxygen hybridization, quantitative local atomic structure, Ni oxidation phase and pore distribution in Ni-rich layered oxide cathodes.

Approaches to synthesize MgO nanostructures for diverse applications

Magnesium oxide remained interesting from long time for several important phenomena like; defect induced magnetism, spin electron reflectivity, broad laser emission etc. Moreover, nanostructures of this material exhibited suitability for different kinds of applications ranging from wastewater treatment to spintronics depending upon their shape and size. In this way, researchers had grown nanostructures in the form of nanoparticles, thin films, nanotubes, nanowalls, nanobelts. Though nanoparticles and thin films are well known form of nanostructures and wide variety of synthesis approaches are available, however, limited methodology for other nanostructures are available. In order to grow these nanostructures in an optimized way an understanding of these methods is essential. Thus, this review article depicts an overview of various approaches for design of different kinds of nanostructures.

Soft X-ray Absorption Spectroscopic Investigation of Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials

Herein, we report the soft X-ray absorption spectroscopic investigation for Li(Ni0.8Co0.1Mn0.1)O2 cathode material during charging and discharging. These measurements were carried out at the Mn L-, Co L-, and Ni L-edges during various stages of charging and discharging. Both the Mn and Co L-edge spectroscopic measurements reflect the invariance in the oxidation states of Mn and Co ions. The Ni L-edge measurements show the modification of the oxidation state of Ni ions during the charging and discharging process. These studies show that eg states are affected dominantly in the case of Ni ions during the charging and discharging process. The O K-edge measurements reflect modulation of metal-oxygen hybridization as envisaged from the area-ratio variation of spectral features corresponding to t2g and eg states.

Local Electronic Structure Perspectives of Nanoparticle Growth: The Case of MgO

Herein, we reported nanoparticle growth from the point of view of the local electronic structure by taking MgO as a prototype material. These nanoparticles were obtained from the sol-gel autocombustion process. The precursor formed in this process was annealed for various temperatures ranging from 300 to 1200 °C for 0.5 and 1 h. It was observed that the amorphous phase occurred in the material synthesized at an annealing temperature of 300 °C for 1 h. This phase transformed to crystalline when the annealing temperature was increased to 350 °C. Crystallite size increased with annealing temperature; however, annealing time did not influence the crystallite size. To get deeper insights of modifications occurring at the atomic scale during crystallization growth, the local electronic structure of synthesized materials was investigated by measuring near-edge X-ray absorption fine structure at Mg, O, N, and C K-edges. These results envisaged that Mg2+ ion coordination improved with the increase of annealing temperature. It was also observed that both annealing time and annealing temperature are sensitive to the local electronic structural changes.

Microstructure, local electronic structure and optical behaviour of zinc ferrite thin films on glass substrate

Zinc ferrite thin films were deposited using a radio-frequency-sputtering method on glass substrates. As-deposited films were annealed at 200°C for 1, 3 and 5 h, respectively. X-ray diffraction studies revealed the amorphous nature of as-grown and annealed films. Thickness of as-deposited film is 96 nm as determined from Rutherford backscattering spectroscopy which remains almost invariant with annealing. Transmission electron microscopic investigations envisaged a low degree of crystalline order in as-deposited and annealed films. Thicknesses estimated from these measurements were almost 62 nm. Roughness values of these films were almost 1-2 nm as determined from atomic force microscopy. X-ray reflectivity measurements further support the results obtained from TEM and AFM. Near-edge X-ray absorption fine structure measurements envisaged 3+ and 2+ valence states of Fe and Zn ions in these films. UV-Vis spectra of these films were characterized by a sharp absorption in the UV region. All films exhibited almost the same value of optical band gap within experimental error, which is close to 2.86 eV.