High voltage stable liquid electrolytes for Li 1+ xMn 2O 4/carbon rocking-chair lithium batteries

Abstract

A high voltage oxidation-resistant electrolyte is required for Li 1+ x Mn 2O 4/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 Li 1+ x Mn 2O 4 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 (LiPF 6) that are kinetically stable up to almost 5 V versus lithium at 55 °C on Li 1+ x Mn 2O 4 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 LiPF 6 and (DMC + EC) (2:1) + 1.5 M LiPF 6 as the best. These compositions have been used in practical Li 1+ x Mn 2O 4/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 LiCoO 2 and LiNiO 2 as well.