No abstract

Li2MnSiO4 has been identified recently as one of the first cathode battery materials that, at least in principle, could exchange more than 1 lithium per redox-active transition metal ion. In this article, we analyze experimentally and by computer simulations based on density functional theory (DFT) why actual experiments have not confirmed these expectations. We show that Li2MnSiO4 is unstable upon delithiation, with a strong tendency to amorphize. Detailed DFT calculations further indicate that it might be possible to obtain a stable material with a reversible exchange of more than one Li per formula unit (FU) by using an appropriate Mn/Fe mixture (solid solution) with a general formula Li2Mn x Fe1 - x SiO4.

Dedicated to Professor Hans Paulsen on the occasion of his 75th birthday (23.XII. 1996) The solid-state structures of three stereoisomers, 1-3, of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-p-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of suficient quality for X-ray single-crystal analysis. The samples of 1-3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. Z), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2-4) in a fashion similar to those already observed for certain cyclo-a-peptides. The stacks of 16-membered rings are held together by four nonlinear C=O ...H-N H-bonds between pairs of molecules (Fig. 5 ) .