Examination of Applying Fluorinated Phosphate Ester to Electrolyte Solvent of the Batteries with LiNi0.5Mn1.5-xTixO4 Cathode

Introduction LiNi0.5Mn1.5O4 is one of the candidates for next generation cathode active material of Li ion batteries, because of large capacity of around 130 mAh/g and the high charge-discharge potential of around 4.65V versus Li. On the other hand, because of the higher potential than conventional cathode active materials, 5V class spinel has the problem of the capacity fading due to decomposition of electrolyte and Mn dissolution. We had studied the improvement of lifetime by Ti substitution for Mn of LiNi0.5Mn1.5O4 3) 4) . To suppress electrolyte decomposition, it was necessary to develop electrolyte solvents which have higher resistance to oxidation. The decomposition reaction of electrolyte may cause gas generation, and it can cause swelling of cells. At room temperature, amount of gas was not large even in conventional electrolyte, but in the case of operation at elevated temperature large amount of gas generation was a problem. In this report, as a candidate for the electrolyte solvents which have higher resistance to oxidation, we examined fluorinated phosphate ester such as tris(2,2,2trifluoroethyl) phosphate(TTFEP). By results of HOMO value calculation, TTFEP was expected to have higher resistance to oxidation than conventional solvents.