Lithium Salt Effects on Silicon Electrode Performance and Solid Electrolyte Interphase (SEI) Structure, Role of Solution Structure on SEI Formation

Abstract

Silicon electrodes were cycled with electrolytes containing different salts to investigate the effect of salt on the electrochemical performance and SEI structure. Comparable capacity retention were observed for the 1.2 M LiPF6, LiTFSI and LiClO4 electrolytes in ethylene carbonate (EC): dimethyl carbonate (DEC), 1: 1, but severe fading was observed for the 1.2 M LiBF4 electrolyte. The differential capacity plots and EIS analysis reveals that failure of the 1.2 M LiBF4 electrolyte is attributed to large surface resistance and increasing polarization upon cycling. However, when LiBF4 was added as an electrolyte additive (10% LiBF4 and 90% LiPF6), the capacity retention and Coulombic efficiency were improved. The SEI was analyzed by FTIR and XPS for each electrolyte. Both spectroscopic methods suggest that the main components of the SEI are lithium ethylene dicarbonate (LEDC) and Li2CO3 in the 1.2 M LiPF6, LiTFSI and LiClO4 electrolytes, while an inorganic-rich SEI, composed of LiF and borates, was generated for both the 1.2 M LiBF4 electrolyte and the 10% LiBF4 electrolyte. The chemical composition of the SEIs and corresponding electrochemical performance of the Si electrodes were strongly correlated with electrolyte solution structure. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.