The Influence of the Solid-Electrolyte Interphase on Polyimide Anodes Probed by Operando Infrared Spectroscopy

The formation of the solid-electrolyte interphase (SEI) plays a critical role in the electrochemical performance and cycling stability of organic anode materials in lithium-ion batteries. In this study, we employ operando attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to investigate the real-time dynamics of SEI formation on polyimide-based organic anodes during charging–discharging cycles. By comparing two commonly used carbonate-based and ether-based electrolytes, we reveal distinct differences in the composition and characteristics of the SEI. These distinct SEI characteristics lead to markedly different electrochemical performances. In ether-based electrolytes, the SEI is predominantly inorganic, facilitating efficient ion transport. The rapid capacity fade is predominated by the irreversible lithium-ion insertion reactions of aromatic ring structures. On the other hand, in carbonate-based electrolytes, the SEI is rich in organic components, leading to higher impedance. In this case, both irreversible carbonyl enolization and lithium-ion insertion into aromatic rings contribute to the rapid capacity fade.