New promising lithium malonatoborate salts for high voltage lithium ion batteries

Three new lithium salts, lithium difluoro-2-methyl-2-fluoromalonatoborate (LiDFMFMB), lithium difluoro2- ethyl-2-fluoromalonatoborate (LiDFEFMB), and lithium difluoro-2-propyl-2-fluoromalonatoborate (LiDFPFMB), have been synthesized and evaluated for application in lithium ion batteries. These new salts are soluble in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (1 : 2 by wt) and 1.0 M salt solutions can be easily prepared. The ionic conductivities of these new salts are close to those of LiBF4 and LiPF6. Cyclic voltammograms reveal that these new salt based electrolytes can passivate both natural graphite and high voltage spinel LiNi0.5Mn1.5O4 (LNMO) to form effective solid electrolyte interphases (SEIs). In addition, these new salt-based electrolytes exhibit good cycling stability with high coulombic efficiencies in both LiNi0.5Mn1.5O4 and graphite based half-cells and full cells.