Effective SEI Formation via Phosphazene-Based Electrolyte Additives for Stabilizing Silicon-Based Lithium-Ion Batteries

Silicon, as potential next-generation anode material for high-energy lithium-ion batteries (LIBs), suffers from substantial volume changes during (dis)charging, resulting in continuous breakage and (re-)formation of the solid electrolyte interphase (SEI), as well as from consumption of electrolyte and active lithium, which negatively impacts long-term performance and prevents silicon-rich anodes from practical application. In this work, fluorinated phosphazene compounds are investigated as electrolyte additives concerning their SEI-forming ability for boosting the performance of silicon oxide (SiOx)-based LIB cells. In detail, the electrochemical performance of NCM523 || SiOx/C pouch cells is studied, in combination with analyses regarding gas evolution properties, post-mortem morphological changes of the anode electrode and the SEI, as well as possible electrolyte degradation. Introducing the dual-additive approach in state-of-the-art electrolytes leads to synergistic effects between fluoroethylene carbonate and hexafluorocyclotriphosphazene-derivatives (HFPN), as well as enhanced electrochemical performance. The formation of a more effective SEI and increased electrolyte stabilization improves lifetime and results in an overall lower cell impedance. Furthermore, gas chromatography-mass spectrometry measurements of the aged electrolyte with HFPN-derivatives as an additive compound show suppressed ethylene carbonate and ethyl methyl carbonate decomposition, as well as reduced trans-esterification and oligomerization products in the aged electrolyte.

Automated summary

This study investigates the effect of fluorinated phosphazene compounds as electrolyte additives on the formation of the solid electrolyte interphase (SEI) in silicon oxide (SiOx)-based lithium-ion batteries. The results show that the dual-additive approach using fluoroethylene carbonate and hexafluorocyclotriphosphazene-derivatives (HFPN) in state-of-the-art electrolytes leads to synergistic effects, enhancing the electrochemical performance and stabilizing the electrolyte. Furthermore, using HFPN derivatives as an additive compound suppresses the decomposition of the electrolyte. This study is of great significance for improving the performance and practical application of lithium-ion batteries.