13C NMR Spectroscopic, CV, and Conductivity Studies of Propylene Carbonate-Based Electrolytes Containing Various Lithium Salts

The ion-solvent and ion-ion interactions, oxidative electrochemical stabilities, and ionic mobilities of a series of lithium salt electrolytes with commonly used electrolyte solvents, propylene carbonate (PC) and dimethyl carbonale (DMC), have been studied using ¹³ C nuclear magnetric resonance (NMR) spectroscopy, cyclic voltammetry (CV), and ionic conductivity measurements. The coordinating ability of PC toward lithium salts is significantly higher than that of DMC as shown by the relatively large deshielding of the carbonyl carbon of PC over that of DMC. We have also prepared a novel electrolyte, lithium tetrakis(trifluoromethanesulfonato)gallate [LiGa(OTf) ₄ ], and investigated its relative binding to PC by ¹³ C NMR spectroscopy. The latter salt showed significant deshielding of the carbonyl carbon of PC compared to the other salts studied, including the conventional LiPF ₆ . However, its conductivity is not enhanced to the same extent and is comparable to that of LiBF ₄ . The CVs show their relative stabilities toward oxidation around 4.5 V and reduction close to lithium potentials. All electrolytes studied here have good electrochemical stability from 0.1 to 5.0 V vs. Li ⁺ /Li, and are suitable for applications in lithium-ion cells.