Novel SEI-Forming Electrolyte Additives for Improved Performance of Silicon-Based Anodes

Abstract

The broad commercial application of high capacity silicon (Si)-based anodes for lithium ion batteries (LIBs) is still hindered by their poor cycling stability caused by large volume changes upon lithiation/delithiation and by the associated continuous electrolyte decomposition and active lithium loss. One suitable strategy to improve the electrochemical performance is to develop improved electrolyte formulations resulting in an efficient solid electrolyte interphase (SEI) formation. A recent study [1] has shown that the addition of 2 wt-% of 3-methyl-1,4,2-dioxazol-5-one (MDO) to a propylene carbonate (PC)-based electrolyte can significantly improve the cycling stability of lithium nickel manganese cobalt oxide (NMC532)/graphite full cells. Since electrolytes, based only on PC, do not lead to the formation of a stable SEI at the anode, the addition of MDO can be linked to an increased SEI stability, which is necessary for a high cycling stability. In this study, we develop a systematic approach to investigate the electrochemical performance of MDO and its various side chain modified derivatives as additives for carbonate-based electrolytes in LIB cells with silicon-carbon (Si-C) composite anodes. Our results show that the addition of MDO improves the cycling stability of Si-C/NMC622 cells in comparison to the state-of-the-art additives, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The systematic evaluation of the electrochemical performance of MDO and its analogues, such as 3-phenyl-1,4,2-dioxazol-5-one (PDO), was done using a cycling protocol adapted from Tornheim et al [2]. This method enables the concurrent determination of the electrode capacity retention and area specific impedance (ASI). Post mortem analysis is performed in conjunction with computational studies to understand the decomposition mechanism. [1] S. Röser, A. Lerchen, L. Ibing, X. Cao, J. Kasnatscheew, F. Glorius, M. Winter, R. Wagner, Chem. Mater. 2017, 29, 7733-7739. [2] A. Tornheim, C. Peebles, J. A. Gilbert, R. Sahore, J. C. Garcia, J. Bareño, D. P. Abraham, J. Power Sources 2017, 365, 201-209.