Rechargeable Li1 + x Mn2 O 4 / Carbon Cells with a New Electrolyte Composition: Potentiostatic Studies and Application to Practical Cells

Abstract

To improve the high temperature performance of Li[sub 1+x]Mn[sub 2]O[sub 4]/carbon rocking-chair secondary batteries the authors searched for and identified a new electrolyte composition whose range of stability extends up to 4.9 V vs Li at room temperature and 4.8 V vs Li at 55 C for the Li[sub x]Mn[sub 2]O[sub 4] material. The behavior of the M = LiMn[sub 2]O[sub 4] composite new electrolyte interface at high voltage (4.2 to 5.1 V vs Li) shows the superposition of two phenomena: (i) an irreversible behavior due to a very slow electrolyte oxidation caused by the large surface area of carbon black (mixed with the Li[sub x]Mn[sub 2]O[sub 4] active material to improve the conductivity) and (ii) two reversible Li deintercalation-intercalation processes in the Li[sub x]Mn[sub 2]O[sub 4] spinel structure. In order to evaluate the kinetics of the high voltage phenomena, the behavior of the LiMn[sub 2]O[sub 4]/new electrolyte interface was investigated as a function of time and temperature. The electrolyte oxidative degradation is a well-stabilized reaction with nontime evolving kinetics, and with an activation energy close to 8 kcal/mol. The self-discharge mechanism a local redox process involving electrolyte oxidation at the electrode surface and reversible intercalation of Li in themore » Li[sub x]Mn[sub 2]O[sub 4] spinel structure. The effective stability of this new electrolyte against oxidation allows for better performance of the rocking-chair cells, in terms of cycle-life and self-discharge, over a wider temperature range ([minus]20 to 55 C.)« less