Direct visualization of solid electrolyte interphase on Li4Ti5O12 by in situ AFM

Whether Li4Ti5O12 has a solid electrolyte interphase (SEI) layer on the electrode surface has been the subject of controversy for a long time due to the delicate nature of this SEI layer and the lack of reliable characterization tools. In this paper, we report direct visualization of SEI layer formation on an LTO electrode surface by in situ atomic force microscopy under potential control. Our results showed that no SEI layer formed from EC/DMC based electrolyte in the potential range of 2.5-1.0 V. However, by extending the reduction potential down to zero, it is possible to grow a SEI layer on the LTO surface. The strategy of forming an SEI layer by discharging an LTO anode down to 0 V in the first cycle and then operating the battery in the normal range of 2.5-1.0 V might be a facile method to improve LTO battery performance. Various additives such as Vinylene Carbonate (VC), ethylene sulfate (ES) and fluoroethylene carbonate (FEC) were used as additives to evaluate their effect on SEI layer formation.