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

Abstract

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.

Vibrational Spectroscopy Insight into the Electrode|electrolyte Interface/Interphase in Lithium Batteries

“…The aim of a fundamental study by Cave et al. [ 103 ] with in situ ATR‐FTIR was to investigate the ion‐pairing dynamics and kinetics of interfacial ion speciation during Li‐ion storage in TiO 2 , as important influencing parameters on the cell performance. For example, with PC as electrolyte solvent, exfoliation in graphite electrodes and PC decomposition occurs, whereas with EC exfoliation is mitigated and a stable SEI is formed.…”

“…Reproduced with permission. [103] Copyright 2021, American Chemical Society. electrolyte signal are observed.…”

“…Schematic depiction of a fast insertion into the negative electrode of Li-ions extracted from a contact ion pair and slow insertion of Li-ions extracted from a completely electrolyte-dissolved Li-ion in 1 m LiClO 4 in acetonitrile and corresponding salt (unpaired perchlorate at 1102 cm −1 and paired 1134 cm −1 ) and solvent (free nitrile at 2253 cm −1 and Li-coordinated nitrile at 2276 cm −1 ) peaks. Reproduced with permission [103]. Copyright 2021, American Chemical Society.…”

Fast‐Charging Strategies for Lithium‐Ion Batteries: Advances and Perspectives

“…At higher charging rates, an increase in local Li + consumption and accumulation due to insufficient ion transport is observed. In addition, Schlenker's team [92] found the kinetic correlation between interfacial ion morphology and Li storage by analyzing ATR and FTIR electrochemical data (Figure 6d). Compared with fully solvated Li, Li extraction from contacting ion pairs (CIPs) may be kinetically more feasible, thereby contributing to the fast‐charging.…”

“…d) When a potential of À 1 V (vs. OCP) is applied to 1.0 M lithium perchlorate (LiClO 4 ) in acetonitrile (ACN) using the in-situ cell, the concentration of paired/unpaired perchlorate and coordinated/uncoordinated ACN changes at the SEI. Reproduced with permission from ref [92]…”