Solvation\nEnvironment and Interface Dynamics of Li<sub>2</sub>B<sub>12</sub>H<sub>12</sub> and Li<sub>2</sub>B<sub>12</sub>F<sub>12</sub> Electrolytes\nUncovered by Theory and O

In this work, we\nevaluated two closo-borate salts (Li<sub>2</sub>B<sub>12</sub>H<sub>12</sub> and Li<sub>2</sub>B<sub>12</sub>F<sub>12</sub>) in propylene\ncarbonate from theoretical and experimental\nperspectives to understand how the coordination environment influences\ntheir spectroscopic and electrochemical properties. The coordination\nenvironments of the closo-borate salts were modeled via density functional\ntheory (DFT) and molecular dynamics (MD). Vibrational spectra calculated\nfrom the predicted coordination environments are in agreement with\nexperimentally measured steady-state FTIR data. This theoretical investigation\nalso suggested that Li<sub>2</sub>B<sub>12</sub>F<sub>12</sub> would\npossess a higher ionic conductivity than Li<sub>2</sub>B<sub>12</sub>H<sub>12</sub>, which was corroborated experimentally. Additionally,\nan electrochemical cell was designed and fabricated that enabled operando\noptical and FTIR spectroelectrochemical (OP-IR-SEC) measurements.\nThis allowed for the simultaneous measurement of the relative changes\nof species at a lithium electrode-liquid electrolyte interface and\nthe visualization of lithium plating at the electrode surface. This\ntechnique could provide new chemical insights and potentially link\noptical changes at the electrode–electrolyte interface to specific\nchemical species in similar electrochemical systems. The Li<sub>2</sub>B<sub>12</sub>F<sub>12</sub> electrolyte was found to have a higher\nthermal stability, which may find utility in applications for batteries\nthat are subject to high-temperature conditions.