Interface Engineering Regulation by Improving Self-Decomposition of Lithium Salt-Type Additive using Ultrasound

Lithium salt-type additives have triggered widespread concern because of their excellent film-forming properties to construct a solid electrolyte interphase (SEI) with high stability and low impedance. However, little attention has been paid to enhancing the utilization efficiency of the expensive lithium salt-type additives. Herein, the main factor limiting the decomposition of lithium difluoro bis(oxalate) phosphate (LiDFBOP) during the initial SEI formation is clarified. Combining the electrochemical analysis results and quantum chemistry calculations, it is inferred that LiDFBOP preferentially decomposes and generates soluble products accumulating on the graphite surface due to diffusion control kinetics. The excessive aggregation of these products on the electrode inhibits the subsequent continuous decomposition of LiDFBOP. An ultrasound auxiliary method is developed to accelerate the soluble product diffusion and promote the reduction decomposition of LiDFBOP increasing the inorganics content of Li2C2O4 and LiF in the formed SEI. Accordingly, the cell performance is greatly improved compared with that without ultrasound: Li/graphite cells with ultrasound can retain 60.60% of initial capacity after 500 cycles at 1C. This work not only pioneers the study of improving the utilization efficiency of additives contributing to reducing the electrolytes cost but also has direct guiding significance in the targeted regulation of interface properties. This work pioneers the research on improving the utilization efficiency of expensive lithium salt-type additives. By employing ultrasound auxiliary method which accelerates the diffusion of soluble products accumulated on the graphite surface, the self-decomposition of lithium difluoro bis(oxalate) phosphate is promoted. This results in a dense, inorganics-rich, and Li+-conductive solid electrolyte interphase, improving the cycle performance of Li/graphite cells.image