Tailoring Electrolyte Additives with Synergistic Functional Moieties for Silicon Negative Electrode-Based Lithium Ion Batteries: A Case Study on Lactic Acid O-Carboxyanhydride

Silicon (Si) has attracted much attention to be applied as a negative electrode (N) material for lithium ion batteries (LIBs) with increased energy density. However, the huge volume changes during (de-)lithiation of the Si, accompanied with the breakdown of the initially formed solid electrolyte interphase (SEI), result in the gradual consumption of active lithium and electrolyte and, hence, a poor cycling performance of LIBs with Si-based N. The addition of various electrolyte additives was proven to be able to reduce the active lithium consumption by the formation of a more effective/flexible and, therefore, better protecting SEI on the Si. Within this study, we synthesize the new electrolyte additive lactic acid O-carboxyanhydride (lacOCA), which is designed to incorporate two different moieties within its structure, that both show to function as effective SEI additives. The addition of small amounts of 2 wt % of lacOCA to the baseline electrolyte significantly improves the electrochemical performance of NMC-111||Si full cells in terms of discharge capacity retention and Coulombic efficiency. The lacOCA also outperforms the comparable additives lactide and diethyl dicarbonate, which are chosen to individually represent the moieties incorporated within the lacOCA structure, proving the synergistic effect of the two different moieties, when in one molecule. Ex situ investigations of the SEI by means of X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy reveal that the SEI formed by lacOCA is mainly composed of poly(lactic acid) and lithium carbonate, which enables a significant reduced consumption of active lithium during charge/discharge cycling of the NMC-111||Si full cells.