Solvation Environment and Interface Dynamics of Li₂B₁₂H₁₂ and Li₂B₁₂F₁₂ Electrolytes Uncovered by Theory and Operando...

In this work, we evaluated two closo-borate salts (Li₂B₁₂H₁₂ and Li₂B₁₂F₁₂) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li₂B₁₂F₁₂ would possess a higher ionic conductivity than Li₂B₁₂H₁₂, which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode-electrolyte interface to specific chemical species in similar electrochemical systems. The Li₂B₁₂F₁₂ electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.