Controlling oxygen coordination and valence of network forming cations

Understanding the structure-property relationship of glass material is still challenging due to a lack of periodicity in disordered materials. Here, we report the properties and atomic structure of vanadium phosphate glasses characterized by reverse Monte Carlo modelling based on neutron/synchrotron X-ray diffraction and EXAFS data, supplemented by Raman and NMR spectroscopy. In vanadium-rich glass, the water durability, thermal stability and hardness improve as the amount of P2O5 increases, and the network former of the glass changes from VOx polyhedra to the interplay between VOx polyhedra and PO4 tetrahedra. We find for the first time that the coordination number of oxygen atoms around a V4+ is four, which is an unusually small coordination number, and plays an important role for water durability, thermal stability and hardness. Furthermore, we show that the similarity between glass and crystal beyond the nearest neighbour distance is important for glass properties. These results demonstrate that controlling the oxygen coordination and valence of the network-forming cation is necessary for designing the properties of glass

In situ NMR observation of the lithium extraction/insertion from LiCoO2 cathode

Rechargeable lithium-ion batteries (LIBs) are currently accepted to be one of the most suitable energy storage resources in portable electronic devices because of their high gravimetric and volumetric energy density. To understand the behavior of Li^{+} ions on electrochemical lithium extraction/insertion process, we performed in situ^{7}Li nuclear magnetic resonance (NMR) measurements for LiC_{o}O_{2} cathode in a plastic cell battery, and the spectral evolutions of the ^{7}Li NMR signal of Li_{x}C_{o}O_{2} (0 ≤ x ≤ 1) were well investigated. Very narrow solid solution region of Li_{x}C_{o}O_{2} (∼0.99 ≤ x < 1) was explicitly defined from the large intensity reduction of Li_{x}C_{o}O_{2} signal at ∼0 ppm, which is related to the localized nature of the electronic spin of paramagnetic Co^{4+} ion formed at the very early delithiation stage. With further decreasing the signal intensity of LiC_{o}O_{2} , a Knight-shifted signal corresponding to an electrically conductive Li_{x}C_{o}O_{2} phase emerged atx = 0.97, which then monotonously decreased in intensity for x < 0.75 in accordance with the electrochemical lithium de-intercalation from Li_{x}C_{o}O_{2}. These observations acquired in situ fully confirm the earlier studies obtained in ex situ measurements, although the present study offers more quantitative information. Moreover, it was shown that the peak position of the NMR shift for Li_{x}C_{o}O_{2} moved as a function of lithium content, which behavior is analogous to the change in its c lattice parameter. Also, the growth and consumption of dendritic/mossy metallic lithium on the counter electrode was clearly observed during the charge/discharge cycles

Correlative Analysis of Ion Concentration Profile and Surface Nanoscale Topography Changes using Operando Scanning Ion Conductance Microscopy

Although various spectroscopic methods have been developed to capture the ion concentration profile changes, it is still difficult to visualize the ion concentration profile and surface topographical changes simultaneously during the charging/discharging of LIBs. To tackle this issue, we have developed an operando scanning ion-conductance microscopy (SICM) method that can directly visualize an ion concentration profile and surface topography using a SICM nanopipette whilst controlling sample potential or current by potentiostat for characterizing the polarization state during charging/discharging. Using operando SICM on the negative electrode (anode) of LIBs, we have characterized ion concentration profile changes and the reversible volume changes related to the phase transition during cyclic voltammetry (CV) and charge/discharge of the hard carbon anode. Operando SICM is a versatile technique that is likely to be of major value for evaluating correlation of the electrolyte concentration profile and nanoscale surface topography changes

Quantitative Visualization of Salt Concentration Distributions in Lithium-Ion Battery Electrolytes during Battery Operation Using X‑ray Phase Imaging

A fundamental understanding of concentrations of salts in lithium-ion battery electrolytes during battery operation is important for optimal operation and design of lithium-ion batteries. However, there are few techniques that can be used to quantitatively characterize salt concentration distributions in the electrolytes during battery operation. In this paper, we demonstrate that <i>in operando</i> X-ray phase imaging can quantitatively visualize the salt concentration distributions that arise in electrolytes during battery operation. From quantitative evaluation of the concentration distributions at steady states, we obtained the salt diffusivities in electrolytes with different initial salt concentrations. Because of no restriction on samples and high temporal and spatial resolutions, X-ray phase imaging will be a versatile technique for evaluating electrolytes, both aqueous and nonaqueous, of many electrochemical systems

Crystal-Based X-ray Interferometry and Its Application to Phase-Contrast X-ray Imaging, Z_eff Imaging, and X-ray Thermography

Crystal-based X-ray interferometry (CXI) detects X-ray phase shifts by using the superposition of waves, and its sensitivity is the highest among the other X-ray phase-detecting methods. Therefore, phase-contrast X-ray imaging (PCXI) using CXI has the highest density resolution among the PCXI methods and enables fine, non-destructive observation with a density resolution below sub-mg/cm3. It has thus been applied in a wide range of fields, including biology, medicine, geology, and industry, such as visualization of the testis and brains of aged rats with tumors, human embryos at each Carnegie stage, air hydrates in old Antarctic ice, and ion distribution in electrolytes. Novel imaging methods have also been developed to take advantage of its high sensitivity, such as visualization of the effective atomic number (Zeff) and the three-dimensional temperature of samples. This article reviews the principles and history of PCXI and crystal-based X-ray interferometers, as well as a CXI system using synchrotron radiation and its potential applications from biomedical to industrial

Stabilization of the Electronic Structure at the Cathode/Electrolyte Interface via MgO Ultra-thin Layer during Lithium-ions Insertion/Extraction

Degradation mechanism of surface coating effects at the cathode/electrolyte interface is investigated using thin-film model electrodes combined with operando X-ray absorption spectroscopy (XAS). MgO-coated LiCoO[2] thin-film electrodes prepared via pulsed laser deposition at room temperature and high temperature are used as model systems. The MgO coating improves the durability of the cathode during high-potential cycling. Operando total reflection fluorescence XAS reveals that initial deterioration due to reduction of Co ions at the surface of the uncoated-LiCoO[2] thin film upon electrolyte immersion is inhibited by the MgO coating. Operando depth-resolved XAS reveals that the MgO coating suppresses drastic distortions of local structure at the LiCoO[2] surface as observed in the uncoated-LiCoO[2] during charging process. The electronic and local structure changes at the electrode/electrolyte interface for two types of surface coating morphologies are discussed

Thickness estimation of interface films formed on Li_{1−x}CoO2 electrodes by hard X-ray photoelectron spectroscopy

Solid electrolyte interface (SEI) films formed on Li_{1−x}CoO_2 electrodes were observed with hard X-ray photoelectron spectroscopy (HX-PES). This paper particularly focuses on film thickness estimation using HX-PES with theoretical calculation. The validity of the calculation was proven by experiments using model SEI films. The native film formed on a LiCoO2 composite electrode was estimated to be LiF with its thickness of 5 nm. Formation of Co (II) species on top of LiCoO_2 was also indicated. Storage of the electrode at 60 °C brought about considerable film growth (30–40 nm) with carbonate compounds formation. SEI film changes during charging of the LiCoO_2 electrode were also examined. The main component in the film was deduced to be LiF or a kind of fluorite, with its thickness decreased during charging. The SEI formation mechanisms are also elucidated