Study On The Electrolyte Additives For Lithium Ion Batteries

We've known that the electrode/electrolyte interphase (SET) plays an important role in lithium-ion batteries. It determines the safety, self-discharge, power capability, low temperature performance, faradic efficiency, and the irreversible capacity loss for the first charge cycle.In this study, we attempt to probe the relationship between the structures of Li-ion nonaqueous electrolytes and its properties by quantum calculation. In our study, we use frontier orbital energy to stand for electrochemistry stability. When electrons are added or removed from the molecule, they will be added to the LUMO and removed from the HOMO. The lower the unoccupied orbital potential (LUMO) is, the easier the molecule is reduced. We choose two film-forming additives -VA, CMA-through this method. The LUMO energy of VA and CMA is lower than that of EC, PC, DMC and DEC. Thus, VA and CMA are reduced more easily than EC and PC.To EC-based electrolyte, the addition of VA and CMA has result in the capacity increase and the cyclic performance improvement to the Li/MCMB half-cells, and the capacity and coulombic efficiency increase to the Li/LiCoO2 half-cells. The results of EIS show that the impedance of Li/MCMB half-cell is reduced on account of the addition of VA and CMA. SEM and FTIR study indicate that VA and CMA take part in the formation of SEI film, and the component of SEI film has been changed in the presence of VA and CMA, and the contents of ROLi and RCOsLi are reduced.To PC-based electrolyte, the addition of VA and CMA can prohibit the co-intercalation of PC, and improve the cyclic performance of MCMB electrode. The CV study indicate that VA and CMA reduce at about the potential of IV, and the products form a passive film, which cover the surface of MCMB electrode and inhibit the co-intercalation of PC.