Xiaoke Mu

VOCl as a Cathode for Rechargeable Chloride Ion Batteries.

A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189 mAh g(-1) . A reversible capacity of 113 mAh g(-1) was retained even after 100 cycles when cycled at a high current density of 522 mA g(-1) . Such high cycling stability was achieved in chloride ion batteries for the first time, demonstrating the practicality of the system beyond a proof of concept model. The electrochemical reaction mechanism of the VOCl electrode in the chloride ion cell was investigated in detail by ex situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results confirm reversible deintercalation-intercalation of chloride ions in the VOCl electrode.

Mechanical Milling Assisted Synthesis and Electrochemical Performance of High Capacity LiFeBO3 for Lithium Batteries.

Borate chemistry offers attractive features for iron based polyanionic compounds. For battery applications, lithium iron borate has been proposed as cathode material because it has the lightest polyanionic framework that offers a high theoretical capacity. Moreover, it shows promising characteristics with an element combination that is favorable in terms of sustainability, toxicity, and costs. However, the system is also associated with a challenging chemistry, which is the major reason for the slow progress in its further development as a battery material. The two major challenges in the synthesis of LiFeBO3 are in obtaining phase purity and high electrochemical activity. Herein, we report a facile and scalable synthesis strategy for highly pure and electrochemically active LiFeBO3 by circumventing stability issues related to Fe(2+) oxidation state by the right choice of the precursor and experimental conditions. Additionally, we carried out a Mössbauer spectroscopic study of electrochemical charged and charged-discharged LiFeBO3 and reported a lithium diffusion coefficient of 5.56 × 10(-14) cm(2) s(-1) for the first time.

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Transmission electron microscopy (TEM) has been used intensively in investigating battery materials, e.g. to obtain phase maps of partially (dis)charged (lithium) iron phosphate (LFP/FP), which is one of the most promising cathode material for next generation lithium ion (Li-ion) batteries. Due to the weak interaction between Li atoms and fast electrons, mapping of the Li distribution is not straightforward. In this work, we revisited the issue of TEM measurements of Li distribution maps for LFP/FP. Different TEM techniques, including spectroscopic techniques (energy filtered (EF)TEM in the energy range from low-loss to core-loss) and a STEM diffraction technique (automated crystal orientation mapping (ACOM)), were applied to map the lithiation of the same location in the same sample. This enabled a direct comparison of the results. The maps obtained by all methods showed excellent agreement with each other. Because of the strong difference in the imaging mechanisms, it proves the reliability of both the spectroscopic and STEM diffraction phase mapping. A comprehensive comparison of all methods is given in terms of information content, dose level, acquisition time and signal quality. The latter three are crucial for the design of in-situ experiments with beam sensitive Li-ion battery materials. Furthermore, we demonstrated the power of STEM diffraction (ACOM-STEM) providing additional crystallographic information, which can be analyzed to gain a deeper understanding of the LFP/FP interface properties such as statistical information on phase boundary orientation and misorientation between domains.

Solution Growth of Ultralong Gold Nanohelices

Metallic nanohelices are extremely rare and, to date, have never been synthesized by a direct solution method. In this work, we report ultralong Au nanohelices grown in solution under ambient conditions. They are ultralong with several tens of micrometers in length, with extraordinary aspect ratio (length/diameter greater than 22 300) and the number of pitches (more than 22 000 pitches). The pitch and width are uniform within each helix but vary widely among the helices. Crystal analyses showed that the facets, twin boundaries, grain sizes, and orientations are aperiodic along the helices. The apparent smooth curving is only possible with a large number of surface steps, suggesting that these structural features are the mere consequence of the helix formation rather than the cause. We propose that the nanowires are formed by the active surface growth mechanism and that the helicity originates from the random and asymmetrical blocking of nuclei embedded within the floccules of ligand complexes, in the form of either asymmetric binding of ligands or asymmetric diffusion of growth materials through the floccules. The separate growth environment of these nuclei causes constant helicity within each helix but differing helicity among the individuals. The embedding also provides a robust environment for the sustained growth of the nanohelices, leading to their record length and consistency.

Radial distribution function imaging by STEM diffraction: Phase mapping and analysis of heterogeneous nanostructured glasses.

Characterizing heterogeneous nanostructured amorphous materials is a challenging topic, because of difficulty to solve disordered atomic arrangement in nanometer scale. We developed a new transmission electron microscopy (TEM) method to enable phase analysis and mapping of heterogeneous amorphous structures. That is to combine scanning TEM (STEM) diffraction mapping, radial distribution function (RDF) analysis, and hyperspectral analysis. This method was applied to an amorphous zirconium oxide and zirconium iron multilayer system, and showed extreme sensitivity to small atomic packing variations. This approach helps to understand local structure variations in glassy composite materials and provides new insights to correlate structure and properties of glasses.

Tailoring Surface Frustrated Lewis Pairs of In2O3−x(OH)y for Gas‐Phase Heterogeneous Photocatalytic Reduction of CO2 by Isomorphous Substitution of In3+ with Bi3+

Abstract Frustrated Lewis pairs (FLPs) created by sterically hindered Lewis acids and Lewis bases have shown their capacity for capturing and reacting with a variety of small molecules, including H2 and CO2, and thereby creating a new strategy for CO2 reduction. Here, the photocatalytic CO2 reduction behavior of defect‐laden indium oxide (In2O3− x(OH)y) is greatly enhanced through isomorphous substitution of In3+ with Bi3+, providing fundamental insights into the catalytically active surface FLPs (i.e., In—OH···In) and the experimentally observed “volcano” relationship between the CO production rate and Bi3+ substitution level. According to density functional theory calculations at the optimal Bi3+ substitution level, the 6s2 electron pair of Bi3+ hybridizes with the oxygen in the neighboring In—OH Lewis base site, leading to mildly increased Lewis basicity without influencing the Lewis acidity of the nearby In Lewis acid site. Meanwhile, Bi3+ can act as an extra acid site, serving to maximize the heterolytic splitting of reactant H2, and results in a more hydridic hydride for more efficient CO2 reduction. This study demonstrates that isomorphous substitution can effectively optimize the reactivity of surface catalytic active sites in addition to influencing optoelectronic properties, affording a better understanding of the photocatalytic CO2 reduction mechanism.

Low temperature structural stability of Fe90Sc10 nanoglasses

ABSTRACT The structural stability of Fe90Sc10 nanoglasses has been studied by means of low temperature crystallization. Specimens were annealed in situ in a transmission electron microscope, and ex situ in an ultra-high vacuum tube-furnace. Both studies led to similar results. The structure of the Fe90Sc10 nanoglasses was stable for up to 2 h when annealed at 150°C. Annealing the Fe90Sc10 nanoglasses at higher temperature resulted in the formation of the nanocrystalline bcc-Fe(Sc). Impact statement The structural evolution of Fe90Sc10 nanoglasses has been studied in detail during low temperature annealing. Our results indicate that the nanostructure of Fe90Sc10 nanoglasses is quite stable at low temperature. GRAPHICAL ABSTRACT

Graphitization and Growth of free-standing Nanocrystalline Graphene using In Situ Transmission Electron Microscopy

Graphitization of polymers is an effective way to synthesize nanocrystalline graphene on different substrates with tunable shape, thickness and properties [1]. The catalyst free synthesis results in crystallite sizes on the order of few nanometer, significantly smaller compared to commonly prepared polycrystalline graphene [2]. Even though this method provides the flexibility of graphitizing polymer films on different substrates, substrate free graphitization of freestanding polymer layers has not been studied yet. For the first time, we report on the thermally induced graphitization and domain growth of free standing nanocrystalline graphene thin films using in situ TEM techniques to study the different processes contributing to the graphene growth.

Comparison of energy filtered TEM spectra image and automated crystal orientation mapping in LiFePO 4 /FePO 4 phase mapping

Lithium iron phosphate (LiFePO 4, LFP) is one of the most promising cathode materia ls for the next generation of Li ion batteries and attracts great a ttentions. Experimental mapping the lithiated (LFP) and delithiated phase (FePO 4, FP) at nanoscale resolution provides knowledge on the microscopic mechanism of the reaction processes during electric al cycling, which is crucial to improve the limits of this material. Versatile scanning / transmission el ectron microscopy (S/TEM) techniques, due to the advantage of intrinsic imaging ability by the elect ron optics, have attracted extreme interest in high resolution phase mapping. The methods are generally sorted into two kinds: one is based on electron energy loss spectroscopy (EELS), such as energy fil tered TEM (EFTEM) [1], relying on the chemical information in the energy spectra; the other is aut omated crystal orientation mapping (ACOM) [2], originally designed for orientation analysis of nan ocrystalline materials [3], relying on the crystallographic information recorded in diffractio n patterns. However, so far, there is no strongly convincing evidence indicating the consistency betw e n the chemical and the crystallographic information in the phase map, because of lacking co mparison of the results between the two kind methods.

Radial Distribution Function Imaging by Diffraction Scanning Electron Microscopy

1. Institut für Nanotechnology (INT), Karlsruhe Insti tu e of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany 2. Helmholtz-Institute Ulm for Electrochemical Energy Storage (HIU), Karlsruhe Institute of Technology (KIT), 89081 Ulm, Germany 3. Karlsruhe Nano Micro Facility (KNMF), Karlsruhe In stitute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany 4. Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology (NJUST), Nanjing, China