Ion-Pairing Dynamics Revealed by Kinetically Resolved In Situ FTIR Spectroelectrochemistry during Lithium-Ion Storage

Understanding the kinetics of interfacial ion speciation could inform battery designs. However, this knowledge gap persists, largely due to the challenge of experimentally interrogating the evolution of ions near electrode interfaces in a sea of bulk signals. We report here the very first kinetically resolved correlation between interfacial ion speciation and lithium-ion storage in a model system, by applying global target analysis to in situ attenuated total reflectance (ATR) Fourier-Transform infrared (FTIR) spectroelectrochemical data. Our results suggest that it may be more kinetically viable for lithium to be extracted from contact ion pairs (CIPs) to contribute to faster electrode charging compared to fully solvated lithium. As the search for fast-charging lithium-ion batteries and supercapacitors wages on, this discovery suggests that manipulating the ion pairing within the electrolyte could be one effective strategy for promoting faster-charging kinetics.