Insights into the selection of SiO bond containing electrolyte additives for Si-based lithium-ion batteries

Abstract

Coupling high-capacity silicon-based anode materials with ternary cathode materials is currently the most effective strategy to improve the energy density of lithium-ion batteries. However, the unstable interfaces between both electrodes and electrolyte impede this process. To address this issue, multifunctional additives incorporating SiO bonds have been widely adopted to bolster the stability of the solid/cathode electrolyte interface (SEI/CEI). Nevertheless, there is scanty research regarding the impact of the quantity and variety of functional groups within these multifunctional additives, which poses challenges for the efficient selection of additives and the tailoring of SEI/CEI. In this study, a series of multifunctional additives with SiO bonds were scrutinized, evaluating their chemical characteristics alongside their effects on the structural durability, interface properties, and electrochemical performance of silicon anodes. The results revealed that differences in molecular structure significantly affect their capacity to suppress LiPF₆ hydrolysis by eliminating HF/H₂O through SiO bonds, with this capability being inversely correlated with the number of SiO bonds present. Moreover, excessive SiO bonds resulted in elevated molecular weight, increased internal resistance, and diminished cell longevity. Notably, additives containing aromatic rings, -CF₃ and CN groups enhanced the SEI robustness and extended the cycle life of silicon anodes. Further investigations demonstrated that this type of additive significantly improves the CEI stability of the NCM622 cathode. Consequently, it enabled an nSi║NCM622 full cell to retain 89.4 % of its capacity after 100 cycles at 1.0C. This study provides valuable insights into the strategic selection and effective utilization of multifunctional additives containing SiO bonds in silicon-based lithium-ion batteries.