Carbon Materials for Lithium Sulfur Batteries—Ten Critical Questions

Lithium–sulfur batteries are among the most promising electrochemical energy storage devices of the near future. Especially the low price and abundant availability of sulfur as the cathode material and the high theoretical capacity in comparison to state‐of‐the art lithium‐ion technologies are attractive features. Despite significant research achievements that have been made over the last years, fundamental (electro‐) chemical questions still remain unanswered. This review addresses ten crucial questions associated with lithium–sulfur batteries and critically evaluates current research with respect to them. The sulfur–carbon composite cathode is a particular focus, but its complex interplay with other hardware components in the cell, such as the electrolyte and the anode, necessitates a critical discussion of other cell components. Modern in situ characterisation methods are ideally suited to illuminate the role of each component. This article does not pretend to summarise all recently published data, but instead is a critical overview over lithium–sulfur batteries based on recent research findings.     

X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Lanthanide transport in stabilized zirconias: interrelation between ionic radius and diffusion coefficient

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1,286 and 1,600 degrees C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and is not strongly affected by the type of lanthanide. The results were correlated with defect energy calculations of the lanthanide diffusion enthalpy using the Mott-Littleton approach. An association enthalpy of cation vacancies with oxygen vacancies of about 1 eV (96 kJ/mol) was deduced in the case of CSZ, while there is no association in the case of YSZ. Furthermore, the change in diffusion coefficients can be correlated to the interaction parameter for the interaction between the lanthanide oxide with zirconia: The higher the interaction parameter, the higher the lanthanide diffusion coefficient.     

Self-diffusion in Mg2SiO4 (forsterite) at high temperature

Summary The use of neutral primary particles for secondary ion mass spectrometry (NPB-SIMS) makes it possible to analyse the isotope concentration profiles of all constituent elements in Mg₂SiO₄ simultaneously. The results indicate

---

Selbstdiffusion in Mg₂SiO₄ (Forsterit) bei hoher Temperatur: Modelluntersuchung für SIMS-Analysen an keramischen Oberflächen

     

Computer modelling of ion migration in zirconia

Defect structure and migration pathways of cations in cubic zirconia (ZrO₂) have been calculated using two computer modelling techniques. The first is based on the Mott–Littleton method, which considers defects to be embedded in an otherwise perfect crystal, and the second is the supercell approach, which allows finite defect concentrations to be modelled. Using the first approach, migration pathways for both intrinsic and dopant cations have been calculated. Activation energies ranging from 3.1 to 5.8?eV have been calculated assuming a vacancy mechanism. For highly charged dopants a curved pathway was found to be favoured over a straight pathway. The effect of stabilizer concentration on the properties of the system investigated has been analysed using the supercell method; 3 × 3 × 3 and 4 × 4 × 4 supercells containing 3–40?mol% calcia (CaO) or yttria (Y₂O₃) have been constructed assuming a random distribution of both dopant cations and oxygen vacancies. After relaxation the oxygen vacancies were found to be located adjacent to the zirconium cations in the CaO-doped system, while remaining randomly ordered in the Y₂O₃-doped system. Also cation vacancies were created, and after relaxation they were surrounded in all systems (CaO-stabilized ZrO₂ and Y₂O₃-stabilized ZrO₂) on average by 2.7 oxygen vacancies.     

A diffusion-controlled mullite formation reaction model based on tracer diffusivity data for aluminium,silicon and oxygen

This paper compiles all the data from our tracer diffusivity studies in single crystalline 2/1-mullite. As tracers we used the rare stable isotopes ¹⁸O and ³⁰Si and the artificial pseudo-stable isotope ²⁶Al. Secondary-ion mass spectrometry was applied to analyze the depth distribution of the tracer isotopes after the diffusion annealing. An essential result of our tracer diffusivity studies was the very low diffusivity of ³⁰Si compared to the diffusivities of ²⁶Al and ¹⁸O, which are almost equal. Based on this observation, we propose a reaction model for the diffusion-controlled formation of mullite in the solid state, which assumes that the growth kinetics of a mullite layer is mainly controlled by the diffusion of aluminium ions and oxygen ions.     

Improved resolution in two-dimensional 1H NMR spectra of peptides by band-selective, homonuclear decoupling during both the evolution and acquisition periods: application to characterization of the binding of peptides by heparin

Two-dimensional 1H NMR experiments that achieve band-selective, homonuclear decoupling in both the indirectly detected F1 and directly detected F2 dimensions were used to assign the highly overlapped 1H NMR spectrum of the peptide Ac-SRGKARVRAKVKDQTK-NH2, both free in solution and bound to heparin. Band-selective, homonuclear decoupling during the evolution period was achieved using a double pulsed field gradient spin-echo (DPFGSE) with semi-selective shaped pulses; band-selective, homonuclear decoupling during the acquisition period was achieved by time-shared semi-selective shaped pulse decoupling. Regular TOCSY, ROESY and NOESY spectra and TOCSY, ROESY and NOESY spectra measured with band-selective, homonuclear decoupling in the evolution (F1) dimension (BASHD-TOCSY, ROESY and NOESY spectra) and with band-selective, homonuclear decoupling in both the F1 and F2 dimensions (D-(or Double)-BASHD-TOCSY, ROESY and NOESY spectra) are reported and compared for the peptide and its heparin complex. Complete assignment of the 1H-NMR spectra of the free and heparin-complexed peptide was achieved with the high resolution of the D-BASHD-TOCSY, ROESY and NOESY spectra. Characterization of the heparin-complexed peptide is of interest because of the ability of the peptide to neutralize the anticoagulant activity of heparin.