Enhancing Lithium Metal Battery Performance with a Perfluorinated Bisalt Electrolyte Achieving High-Voltage Stability up to 4.8 V

Abstract

The electrolyte holds a pivotal function in modulating and stabilizing the interphase of lithium metal anodes in lithium metal batteries. This study investigates the molecules composition of solvents and their interactions with lithium salts to the develop a perfluorinated bisalt electrolyte. This innovative electrolyte employs ethyl 2-fluoropropionate (EFP) in conjunction with fluoroethylene carbonate (FEC) to modulate the solvent shell structure, enhancing the cooperative effects of the dual lithium salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF₆) (referred to as 15TP). This approach promotes anions aggregation and the development of a robust inorganic-rich electrode/electrolyte interphase layer, efficiently suppressing lithium dendrite growth and stabilizing the ultra-high-nickel LiNi_0.91Co_0.06Mn_0.03O₂ (NCM91) cathode. Compared to commercial electrolytes, the 15TP significantly reduces undesirable side reactions at high-voltages. Its non-flammability, excellent wettability, and broad electrochemical window enable the Li||NCM91 cell to achieve a discharge capacity of 150 mAh g^-1 after 500 cycles at a 4.5 V and a 1 C rate, with a super high average Coulombic efficiency of 99.74%. It retains 85.57% capacity after 100 cycles at 4.7 V and exceeds 80% retention at 4.8 V. The findings provide a novel approach for designing high-voltage electrolytes for lithium metal batteries.