Effect of Surface Termination on Electrochemical Performance of Silicon Thin Films

The surface termination layer of silicon-based lithium-ion anodes is a complex mixture of silicon oxides, hydroxides, and hydrides. The species present reflect the history of the electrode and combine to make each silicon electrode different in its electrochemical performance and reactivity with the electrolyte. This variability creates challenges for silicon-based anodes as it affects SEI formation and stability, columbic efficiency, and irreversible capacity. To elucidate some of the parameters that control surface functionality we used non-aqueous electrodeposition to produce silicon thin films on copper foams. These porous electrodes were studied using Si-29 MAS NMR to correlate the synthetic process and surface functionality with electrochemical performance. We found that the supporting electrolyte salt used has a significant effect on the electrodeposited silicon thin films electrochemical properties. Films deposited using tetrabutylammonium chloride (TBACl) were found to be more crystalline with much higher surface concentration of hydrides, hydroxides and oxides, have lower capacity, and much higher irreversible capacity than films deposited using tetraethylammonium chloride (TEACl). The role of supporting electrolyte salt is hypothesized to be related to the amount of free solvent in the reaction mixture as the TBACl salt has been reported to tie up significantly more solvent due its larger size. (C) The Author(s) 2015. Published by ECS.