Investigation of fluorinated ether-containing electrolytes for high energy-density nickel-rich LiNi0.8Co0.1Mn0.1O2 electrodes

Nickel-rich LiNixCoyMn1-x-yO2 (x >= 0.6, NCM) materials and in particular LiNi0.8Co0.1Mn0.1O2 (NCM811) are considered as the most potential candidates for utilization in the next-generation of high-energy-density lithium-ion batteries (LIBs). However, the NCM811 materials encounter capacity fading during cycling, originating mainly from detrimental positive electrode-electrolyte interface changes. Here, to decrease electrolyte oxidative decomposition during NCM811 cycling process, we select a partially fluorinated ether, such as 1,1,2,2- tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM), as a co-solvent for fluoroethylene carbonate (FEC)-based electrolytes and investigate theirs physicochemical and electrochemical performances in great details for their applications in NCM811 materials. Compared to the FEC-based electrolyte solution without a fluorinated ether co-solvent, the electrolytes with a fluorinated ether co-solvent exhibits an obviously improved cycling and rate properties of the Li/NCM811 cells cycled between 2.7 and 4.3 V. This work also shows that the TTE solvent is prone to both suppress the decomposition of FEC to stabilize the FEC-based electrolyte solution, and be reduced and form a stable interface layer in the highly reactive Li surface.