Distance-Dependent Solid Electrolyte Interphase Control by Electrochemical Pretreatment

A new method to control the morphology and chemical composition of the solid electrolyte interphase (SEI) on the Si anode via electrochemical pretreatment with variation of the distance between the counter electrode and the working electrode has been investigated. This fundamental investigation reveals that the chemical composition and structure of the SEI are dependent on the distance between the electrodes during electrochemical pretreatment. The electrochemical pretreatment in a conventional coin cell or with a narrow gap between the electrodes (0.5 mm) generates a SEI composed of a mixture of Li2CO3 and LiF on the Si anode. However, with a large distance between the electrodes (≥2 mm), a LiF-dominant surface film is generated with well-dispersed LiF nanoparticles (<500 nm), improving the electrochemical performance of the Si anode. This finding provides insight into the potential to use distance between electrodes during electrochemical pretreatment as a method to control the structure and function of the SEI.