Improved Utilization of Lithium Salt Additives in Lithium-Ion Batteries Through Power-Tuned Ultrasound for Stable Solid Electrolyte Interphase Layer Formation

Lithium salt additives, as an important component of lithium-ion batteries (LIBs), suffer from problems of incomplete decomposition and low utilization, causing waste, safety, and environmental pollution. Applying a physical field such as ultrasound during battery formation was proposed to accelerate the decomposition of lithium salt additives such as lithium difluoro bis(oxalate) phosphate (LiDFBOP), but the ultrasonic power seems to critically affect the decomposition efficiency and the components and structure of the solid electrolyte interface (SEI) film because of the exacerbation of side effects. Hence, we explored the effect of different ultrasonic powers and half the amount of lithium salt additives on the decomposition of lithium salt and the components and structure of the generated SEI film, thereby establishing the correlation between ultrasonic power, the amount of lithium salt additives, and electrochemical performance and achieving the goal of 'reducing amount and increasing efficiency' for electrolyte additives. Herein, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and finite element analysis (FEA) were utilized to demonstrate the deposition behavior of reaction products on the electrode surface under varying ultrasonic powers during battery formation, revealing that the SEI film formed under the ultrasonic power of 105 W exhibited the smoothest and most intact morphology. Therefore, the graphite/Li cell during the battery formation of 105 W ultrasonic power with half the amount of lithium salt additives maintained a great capacity retention ratio of 88.49% at 0.2C for 350 cycles, which is higher than other samples. This work provided a solution strategy for reducing the amount of lithium salt additives while generating an SEI film with excellent mechanical properties to enhance the electrochemical performance and save cost by controlling the ultrasonic power, which has great significance for the green and sustainable development of LIBs.