LONG CHAIN 1-ALKYL-3-METHYLIMIDAZOLIUM TETRAFLUOROBORATES AS ELECTROLYTES IN Li-ION BATTERIES

Abstract

ABSTRACT We have determined the electrochemical behavior of a series of long chain 1-alkyl-3-methylimidazolium ionic liquids [(R-mim)BF 4 ], with alkyl groups ranging from pentyl to octyl, and tested them as electrolytes in lithium ion batteries. These ionic liquids present good conductivities and electrochemical windows which make them likely solvents of choice for Li-ion batteries using LiMn 2 O 4 as the cathode. Charge/discharge properties of a Li/ R-mim)BF 4 /LiMn 2 O 4 cell have been evaluated both with the IL as the sole electrolyte and with IL and conducting support. The Li- ion insertion results in IL can be explained on the basis of self aggregation of each long chain 1-alkyl-3-methylimidazolium cation. INTRODUCTION It is well known that progress in lithium-ion batteries relies much on improvements in the electrolyte. Ionic liquids (IL) have become a viable alternative as electrolytes for these devices [1]. In general, the most common electrolytes for Li-ion batteries are a mixture of 1:1 EC/EMC (ethylene carbonate and ethyl methyl carbonate) and LiPF