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.

Automated summary

The study found that electrolytes with TTE and HFPM as cosolvents exhibit significantly improved cycling and rate properties for Li/NCM811 cells cycled between 2.7 and 4.3 V, compared to FEC-based electrolyte solutions without a fluorinated ether cosolvent.