HIGH-VOLTAGE STABLE LIQUID ELECTROLYTES FOR LI1+XMN2O4/CARBON ROCKING-CHAIR LITHIUM BATTERIES

A high voltage oxidation-resistant electrolyte is required for Li1+xMn2O4/carbon rocking-chair cells that need to be charged up to a Voltage higher than 4.3 V. Many electrolyte compositions have been tested for their ability to resist to high voltages on Li1+xMn2O4 electrodes and their ability to maintain high ionic conductivity in a wide temperature range. This survey allowed us to select new electrolyte compositions in the system dimethyl carbonate (DMC)+ethylene carbonate (EC)+lithium hexafluorophosphate (LiPF6) that are kinetically stable up to almost 5 V Versus lithium at 55 degrees C on Li1+xMn2O4 electrodes. Low rate potentiostatic experiments, coupled with coulombmetric measurements in the 4.25-5.1 V range, allowed to select the following compositions: (DMC+EC) (1:2)+1 M LiPF6 and (DMC+EC) (2:1)+1.5 M LiPF6 as the best. These compositions have been used in practical Li1+xMn2O4/carbon rocking-chair batteries and show better performance in terms of cycle life and self-discharge over a wider temperature range. They are compatible with rocking-chair batteries based on LiCoO2 and LiNiO2 as well.