Lithium-Chalkogenidometallate als neue funktionelle Materialien für Lithium-Ionen-Batterien

1. Synthesized Compounds: 27 new compounds were synthesized and stucturally characterized. The different synthesis methods are summarized in the following paragrphs: The high temperature reactions following method 1 proved to be very effective. By simply fusing together the starting materials, new soluable ternary chalcogenidotetrelate salts containing isolated anions were obtained. A purification could easyly be done by an extraction procedure. After drying the product solvates, solvent free polycrystalline phases of the compounds were obtained. By runnig the synthesis under flux conditions according to method 2 qarternary tetrahedral networks were obtained. These compounds are quite stable and unsoluable, therefore they can be purified by simply washing with water. The compounds 8-15 are thermally stable under sublimation conditions and the unsoluable exess of chalcogen can be removed via sublimation. The aim of the solvothermal reactions of method 3 was the synthesis of zeotype networks. Ternary chalcogenidotetrelate salts should be reacted with transitionmetal salts or tetrel(IV) halides as the connecting agents. In most cases no reaction took place at all, or just a simple ion change occured, like for the compounds 20-21. In the cases a connection occured, the connecting agent did not take part in the reaction and the chalcogenidotetrelate anions connected to each other (22-23). Using method 4 the synthesis of the zeotype network Li2[MnGe4Se10] · 8 H2O (26) was achieved. 26 is an important product of this work, due to its large channels in the structure, which possibly enables an ionic conduction. Unfortunately 26 shows a very poor crysallisation behavior and therefore a poor reproducibility for big amounts. It is for that reason that it was not possible to measure the ionic conductivety. Compund 27 was obtained by acidification of a solution of 1. 2. Properties: The ionic conductivity of the compounds 1, A and Edry was investigated via impedance spectroscopy. The conductivity measured for 1 and A were exceptionally high for ternary compounds. The values at ambient temparature were 7·10-5 S·cm-1 for 1 and 2·10-5 S·cm-1 for A . The values were confirmed by solid state NMR experiments and DFT simulations. The simulations also showed vacancy diffusion as the dominant mechanism of the ion transport. The compounds 8 and 9 were prepared as electrodes with lithium metal as counter electrode. The compounds showed a reversible uptake and release of lithium ions. The specific capacity of 8 reaches up to 725 mAh/g and 660 mAh/g after 50 cycles, and thus is very high with an excellent long time stability. Compound 9 shows a slighly less good performance (665 mAh/g starting capacity and 450 mAh/g after 50 cycles). You can see the great potential of the material class as anode materials by comparing the values of both compounds with that of commercial used graphite (maximal capacity 370 mAh/g).