Synthesis and Electrochemical Studies of Aryl-Substituted Group 14 Compounds

Organosilicon and -tin compounds are already used in various industries ranging from surface modifying silicones, thin films for electronic transistors and opto-electronic devices. Future consumer electronics and electric vehicles could also rely on high-performance Li-ion batteries with silicon or tin-based anodes. Their fully lithiated phases Li4.4E(IV) boast theoretical capacities of 4200 mAh g–1 for silicon and 990 mAh g–1 for tin. So far, however, such anodes still suffer from immense volume expansions of up to 400%vol which eventually fractures the material and thus limits cycle-life. These complications are mitigated when the silicon or tin are nanostructured or embedded in carbon (Si/C or Sn/C).
In this work, novel and previously published aryl-substituted silanes and stannanes were synthesised, comprehensively characterised and processed in order to develop nanostructured Si/C or Sn/C anode materials for Li-ion batteries. The silanes and stannanes were substituted with aryl groups such as phenyl, o-tolyl, 2,5-xylyl and 1-naphthyl or, hitherto uncharacterised, mixtures thereof. The effects of substituent bulk on the 29Si chemical shifts, the solid-state interactions in single crystals and the electrochemical properties are discussed. Electrochemical characterisation of aryl silanes was carried out in non-aqueous environment in a purpose-built, optimised cyclic voltammetry cell. Subsequently, the aryl silanes were pyrolysed and the arylstannanes coupled to form Si/C and Sn/C anode materials, respectively. These materials displayed specific capacities exceeding the capacities of state-of-the-art graphite anodes by up to 20% and excellent cyclic stability.