Trichlorosilylated tetrelides [(Cl3Si)3E]− have been prepared by adding 1 equiv of a soluble Cl− salt to (Cl3Si)4Si (E=Si) or 4 Si2Cl6/GeCl4 (E=Ge). To assess their donor qualities, the anions [(Cl3Si)3E]− (E=C, Si, Ge) have been treated with BCl3, AlCl3, and GaCl3. Both BCl3 and GaCl3 give 1:1 adducts with the anionic centers. AlCl3 leads to Cl− abstraction from [(Cl3Si)3E]− with formation of (Cl3Si)4E (E=Si or Ge). (Cl3Si)4Ge is cleanly converted to the perhydrogenated (H3Si)4Ge by use of Li[AlH4]. Another case of Cl− abstraction was observed for [(Cl3Si)3Ge⋅GaCl3]−, which reacts with GaCl3 to afford the neutral dimer [(Cl3Si)3Ge−GaCl2]2.
A one-step non-reactive spray drying approach has been successfully demonstrated to produce hierarchically structured supraparticles of silicon/carbon composite nanoparticles synthesized in the gas-phase for Lithium-ion battery anodes. The produced supraparticles combine the advantages of both nanoparticles and micrometer-sized particles: they inherit nanoparticle-like mechanical stability to resist pulverization but have a reduced surface area and therefore electrolyte contact area. The supraparticles showed very good redispersion stability when processed into electrodes and showed an improved density of the coated layer (increase by 19 %) as compared to silicon/carbon composite nanoparticles. Furthermore, supraparticles exhibited a good first cycle Coulombic efficiency around 86% and a good cycling stability, i.e. 80% of the 3rd cycle capacity was retained after 126 cycles vs only 65.2% after the same number of cycles for the best coating from silicon/carbon composite nanoparticles. We consider this investigation as key finding for the scalable manufacturing of low-cost and dense Si-based anode materials for LIBs and at the same time as an example of how hierarchical electrode structures can make significant impact in electrochemistry.
The combining of the two process steps comminution and chemical reactionI'S realizedin a newly developed apparatus, the so-called reaction-mill. It is an up to 450'C heatable vibration-mill, that is resistant to pressures up to 2 MPa and that has a gas inlet and outlet for running heterogeneous chemical reactions during the process of comminution. The possible accelerations of the vibration-mill exceed up to 65 g and relative amplitudes of maximum 0.14 are adjustable. The advantage of the combination of the two process steps is the utilization of the effectsof comminution exceeding the changes in the dispersity of the solid. The examined heterogeneous non-catalytic gas-solid reaction is the conversion of metallurgical grade (MG) silicon with gaseous hydrogen chloride to give trichlorosilane and silicon tetrachloride. The examinations of the combined hydrochlorination and comminution have shown, that the induction periods in the starting phase of the reaction, carried out singularly, can be reduced to a minimum. Furthermore it could be noticed, that the lower temperature limit, which is necessary to start the reaction, could be lowered from 300°C to 100°C and that the selectivity of the reaction products is influenced by the mechanical energy. On one hand the effects are explained by the changes in the dispersity of the solid during comminution and on the other hand by a mechanical activation of the MG silicon.
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