On the thermal behavior of model Li-LixCoO2 systems containing ionic liquids in standard electrolyte solutions

We report herein on the possibility of using ionic liquids (ILs) as additives to conventional electrolyte solutions, based on alkyl carbonates and LiPF6 for attenuating thermal reactions in Li battery systems. As a model, a Li-Li0.5CoO2 system was used. The ionic liquids chosen included cations based on derivatives of pyrrolidinium and imidazolium. and the anions bioxalato borate (C4O8B-, BOB), (CH3SO2)(2)N- (TFSI), and PF3(C2S5)(3)(-) (FAP). The thermal behavior of solutions alone, solutions with Li metal, Li0.5CoO2 and Li metal + Li0.5CoO2 was studied. It was found that the presence of 10% of ILs, with derivatives of pyrrolidinium cations and FAP or TFSI anions in standard EC-DMC/LiPF6 solutions, improves considerably the thermal stability of Li0.5CoO2 in electrolyte solutions. The onset temperatures of the thermal reactions of Li0.5CoO2 with solution species are higher and their heat evolution is considerably lower, when they contain these ionic liquids as additives. This finding opens the door for further studies and optimization of the use of selected ILs as additives that may improve the safety features of Li-ion batteries. (C) 2008 Elsevier B.V. All rights reserved.