New promising lithium malonatoborate salts for high voltage lithium ion batteries

Abstract

Three new lithium salts, lithium difluoro-2-methyl-2-fluoromalonatoborate (LiDFMFMB), lithium difluoro-2-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 LiNi_0.5Mn_1.5O₄ (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 LiNi_0.5Mn_1.5O₄ and graphite based half-cells and full cells.