Understanding the Behavior of LiCoO2 Cathodes at Extended Potentials in Ionic Liquid–Alkyl Carbonate Hybrid Electrolytes

Abstract

The current electrolyte compositions makes it hard to achieve a high energy density lithium-ion battery based on LiCoO2 chemistry due to the destabilization of the LiCoO2 crystal structure beyond 4.2 V vs Li/Li+ leading to oxygen evolution and electrolyte decomposition. Therefore, electrolyte developments may hold promise for improved performance, for example, if some of the advantageous properties of ionic liquids can be introduced into a carbonate electrolyte system. Here, we report the use of a hybrid electrolyte (HE) system with a LiCoO2 cathode and have observed an excellent electrochemical performance when cycled to 4.4 V vs Li/Li+. This extended potential range produces higher capacity via greater ion insertion/extraction and better structural stability. A discharge capacity of 161 mAh/g (0.7 lithium extraction) was observed in the HE as compared to 128 mAh/g in conventional electrolyte, after 60 cycles. The charge–discharge studies at extended potentials also indicate better capacity retention in ...