Formulation of a New Type of Electrolytes for LiNi1/3Co1/3Mn1/3O2 Cathodes Working in an Ultra-low Temperature Range

A new type of electrolytes for low temperature operation of Li-ion batteries was formulated in this work. Instead of LiPF6, LiBF4 and LiODFB were used to form this new type of electrolytes, although LiPF6 is the mostly chosen solute in the state-of-the-art Li-ion electrolytes. It was found although a LiBF4-based electrolyte had a lower ionic conductivity than that of a LiODFB-based electrolyte, a LiODFB-based electrolyte demonstrated improved low temperature performance. In particular, at -30 degrees C, a Li-ion cell with 1M LiODFB dissolved in a 1:2:5 (wt.) propylene carbonate (PC)/ethylene carbonate (EC)/ethyl methyl carbonate (EMC) mixed solvent delivered 86% of the capacity obtained at 20 degrees C. Furthermore, the cells with a LiODFB-based electrolyte showed lower polarization at -30 degrees C. The above results suggest that beside the ionic conductivity of an electrolyte as a limitation to the low temperature operation of Li-ion batteries, there was interface impedance having effect on it. Analysis of cell impedance revealed that reduced charge-transfer resistance by using LiODFB resulted in improved low temperature performance of Li-ion batteries.