Dinitrile compound containing ethylene oxide moiety with enhanced solubility of lithium salts as electrolyte solvent for high-voltage lithium-ion batteries

A dinitrile compound containing ethylene oxide moiety (4,7-dioxa-1,10-decanedinitrile, NEON) is synthesized as an electrolyte solvent for high-voltage lithium-ion batteries. The introduction of ethylene oxide moiety into the conventional aprotic aliphatic dinitrile compounds improves the solubility of lithium hexafluorophosphate (LiPF 6 ) used commercially in the lithium-ion battery industry. The electrochemical performances of the NEON-based electrolyte (0.8 M LiPF 6  + 0.2 M lithium oxalyldifluoroborate in NEON:EC:DEC, v : v : v  = 1:1:1) are evaluated in graphite/Li, LiCoO 2 /Li, and LiCoO 2 /graphite cells. Half-cell tests show that the electrolyte exhibits significantly improved compatibility with graphite by the addition of vinylene carbonate and lithium oxalyldifluoroborate and excellent cycling stability with a capacity retention of 97 % after 50 cycles at a cutoff voltage of 4.4 V in LiCoO 2 /Li cell. A comparative experiment in LiCoO 2 /graphite full cells shows that the electrolyte (NEON:EC:DEC, v : v : v  = 1:1:1) exhibits improved cycling stability at 4.4 V compared with the electrolyte without NEON (EC:DEC, v : v  = 1:1), demonstrating that NEON has a great potential as an electrolyte solvent for the high-voltage application in lithium-ion batteries.