New halogenated additives to propylene carbonate-based electrolytes for lithium-ion batteries

Lithium cannot be electrointercalated into graphite in an electrolyte containing propylene carbonate (PC) as the only solvent species. In order to improve the cycleability of graphite electrodes in the presence of PC two methods were used: use of solvent mixtures containing PC and halogen-substituted solvent molecules (alpha-bromo-gamma-butyrolactone and methyl chloroformate); impregnation of the graphite electrode by halogenated solvents prior to cycling in PC-based electrolytes. It appears that the reversible capacity is increased by similar to 10% when such halogenated solvent molecules are used. Moreover, the cycleability is dependent on the nature of lithium salt, the concentration of halogen solvent and the specific current. (C) 2000 Elsevier Science Ltd. All rights reserved.