Toward 5 V Li-Ion Batteries: Quantum Chemical Calculation and Electrochemical Characterization of Sulfone-Based High-Voltage Electrolytes

In seeking new sulfone-based electrolytes to meet the demand of 5 V lithium-ion batteries, we have combined the theoretical quantum chemistry calculation and electrochemical characterization to explore several sulfone/cosolvent systems. Tetramethylene sulfone (TMS), dimethyl sulfite (DMS), and diethyl sulfite (DES) were used as solvents, and three kinds of lithium salts including LiBOB, LiTFSI, and LiPF6 were added into TMS/DMS [1:1, (v)] and TMS/DES [1:1, (v)] to form high-voltage electrolyte composites, respectively. All of these electrolytes display wide electrochemical windows of more than 5.4 V, with the high electrolyte conductivities being more than 3 mS/cm at room temperature. It is indicated that to achieve the best ionic conductivity in TMS/DMS cosolvent, the optimized concentrations of lithium salts LiBOB, LiTFSI, and LiPF6 were 0.8, 1, and 1 M, respectively. Furthermore, the vibrational changes of the molecular functional groups in the cosolvents were evaluated by Fourier transform infrared spectroscopy. It is found that lithium salts show strong interaction with the main functional sulfone groups and sulfonic acid ester group, thus playing a vital role in the enhancement of the ionic conductivity and electrochemical stability of the solvent system. These sulfone-based solvents with high electrochemical stability are expected to become a new generation of a high-voltage organic electrolytic liquid system for lithium-ion batteries.