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

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 Si-O 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 Si-O 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 Si-O bonds, with this capability being inversely correlated with the number of Si-O bonds present. Moreover, excessive Si-O bonds resulted in elevated molecular weight, increased internal resistance, and diminished cell longevity. Notably, additives containing aromatic rings, -CF3 and C--N 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 & boxV;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 Si-O bonds in silicon-based lithiumion batteries.