Electrochemical behavior of isocyanate as novel film-forming additive in electrolytes

New sulfone-isocyanate mixed electrolytes based on tetramethylene sulfone(TMS) and p-toluenesulfonyl isocyanate(PTSI) were prepared. Their physiochemical properties and electrochemical behavior on the mesocarbon microbeads electrode(MCMB) were investigated by galvanostatic charge-discharge and cyclic voltammetry(CV). The results show that the electrochemical window of the electrolytes are over 5.0 V. Moreover, the mixed electrolytes even perform good thermal stability. Compared with pure TMS-based electrolytes, the mixed electrolytes show better wettability and improved lithiation/delithiation reversibility. The Li/MCMB half-cell exhibits a specific capacity of over 360 mA5h/g with excellent capacity retention after 50 cycles when combined with a composite electrolyte containing 5%(volume fraction) PTSI because an effective solid electrolyte interface layer is thought to form. The energies of the lowest unoccupied and highest occupied molecular orbitals of PTSI are lower than those of TMS and vinylene carbonate, indicating that PTSI molecules can accept electrons readily and possess a high oxidation potential.