Thomas Leichtweiß

The Detrimental Effects of Carbon Additives in Li10GeP2S12 based Solid-State Batteries

All-solid-state batteries (SSBs) have recently attracted much attention due to their potential application in electric vehicles. One key issue that is central to improve the function of SSBs is to gain a better understanding of the interfaces between the material components toward enhancing the electrochemical performance. In this work, the interfacial properties of a carbon-containing cathode composite, employing Li10GeP2S12 as the solid electrolyte, are investigated. A large interfacial charge-transfer resistance builds up upon the inclusion of carbon in the composite, which is detrimental to the resulting cycle life. Analysis by X-ray photoelectron spectroscopy reveals that carbon facilitates faster electrochemical decomposition of the thiophosphate solid electrolyte at the cathode/solid electrolyte interface-by transferring the low chemical potential of lithium in the charged state deeper into the solid electrolyte and extending the decomposition region. The occurring accumulation of highly oxidized sulfur species at the interface is likely responsible for the large interfacial resistances and aggravated capacity fading observed.

Controlled surface modification of Ti-40Nb implant alloy by electrochemically assisted inductively coupled RF plasma oxidation.

Low temperature metal oxidation induced by plasma in the absence of liquid electrolytes can be useful for the surface preparation of orthopedic devices since residues from these may be harmful and need to be removed before implantation. In this study the oxidation of Ti-40Nb for biomedical application was achieved by employing an inductively coupled radio frequency oxygen plasma. The correlation between the growth mode of the surface oxide and the electric conductivity ratio of the plasma and the oxide phase were studied by varying the sample temperature, oxygen gas pressure and additional bias potential. The plasma treated samples were characterised by confocal laser microscopy, SEM, EBSD, XPS, TEM and ToF-SIMS. The surface energy was determined by contact angle measurements using the Owens-Wendt-Rabel-Kaelble method. Well adhering oxide layers consisting of TiO2 and Nb2O5 with thicknesses between 50 and 150 nm were obtained. Surface roughness values and microstructure indicate that the growth mode of the oxide can be well controlled by the sample temperature and oxygen gas pressure. At temperatures above 450°C a migration of Ti ions towards the surface controls the growth process. A bias potential higher than +50 V causes rough and defective surfaces with high surface energies.

Covalent immobilization of lysozyme onto woven and knitted crimped polyethylene terephthalate grafts to minimize the adhesion of broad spectrum pathogens

Graft-associated infections entirely determine the short-term patency of polyethylene terephthalate PET cardiovascular graft. We attempted to enzymatically inhibit the initial bacterial adhesion to PET grafts using lysozyme. Lysozyme was covalently immobilized onto woven and knitted forms of crimped PET grafts by the end-point method. Our figures of merit revealed lysozyme immobilization yield of 15.7 μg/cm(2), as determined by the Bradford assay. The activity of immobilized lysozyme on woven and knitted PET manifested 58.4% and 55.87% using Micrococcus lysodeikticus cells, respectively. Noteworthy, the adhesion of vein catheter-isolated Staphylococcus epidermidis decreased by 6- to 8-folds and of Staphylococcus aureus by 11- to 12-folds, while the Gram-negative Escherichia coli showed only a decrease by 3- to 4-folds. The anti-adhesion efficiency was specific for bacterial cells and no significant effect was observed on adhesion and growth of L929 cells. In conclusion, immobilization of lysozyme onto PET grafts can inhibit the graft-associated infection.

Li+ Ion Conductors with Adamantane-type Nitridophosphate Anions - β-Li10P4N10 and Li13P4N10X3 with X = Cl, Br

β-Li10 P4 N10 and Li13 P4 N10 X3 with X=Cl, Br have been synthesized from mixtures of P3 N5 , Li3 N, LiX, LiPN2 , and Li7 PN4 at temperatures below 850 °C. β-Li10 P4 N10 is the low-temperature polymorph of α-Li10 P4 N10 and crystallizes in the trigonal space group R3. It is made up of non-condensed [P4 N10 ]10- T2 supertetrahedra, which are arranged in sphalerite-analogous packing. Li13 P4 N10 X3 (X=Cl, Br) crystallizes in the cubic space group Fm3‾m . Both isomorphic compounds comprise adamantane-type [P4 N10 ]10- , Li+ ions, and halides, which form octahedra. These octahedra build up a face-centered cubic packing, whose tetrahedral voids are occupied by the [P4 N10 ]10- ions. The crystal structures have been elucidated from X-ray powder diffraction data and corroborated by EDX measurements, solid-state NMR, and FTIR spectroscopy. Furthermore, we have examined the phase transition between α- and β-Li10 P4 N10 . To confirm the ionic character, the migration pathways of the Li+ ions have been evaluated and the ion conductivity and its temperature dependence have been determined by impedance spectroscopy. XPS measurements have been carried out to analyze the stability with respect to Li metal.