Functional Electrolyte of Fluorinated Ether and Ester for Stabilizing Both 4.5 V LiCoO<sub>2</sub> Cathode and Lithium Metal Anode
Shuangshuang Lin, Jinbao Zhao
Abstract
In our work, fluoroethylene carbonate (FEC) with higher ionic conductivity and oxidative stability has been used to replace ethylene carbonate along with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) added to obtain a trisolvent electrolyte system of 1.2 M LiPF6 in FEC/dimethyl carbonate/HFE (1:1:1 by volume). In addition, on the basis of such an electrolyte, we have also added 0.15 M lithium difluoro(oxalato)borate as a film-forming additive to further stabilize both the cathode and anode, so that a new bifunctional electrolyte of 1.35 M has been obtained. The new electrolyte enables Li||LiCoO2 batteries to maintain nearly 84% capacity after 300 cycles when charged to 4.5 V under the current density of 200 mA g–1. Meanwhile, it can also make Li||Cu half-cells maintain about 98% coulombic efficiency after being charged/discharged 200 times under 1 mA cm–2 current density and 1 mAh cm–2 lithium deposition amount per cycle, showing an obvious advantage in the stability of lithium metal.