科研之友
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摘要
Anion solvation in electrolytes can largely change the electrochemical performance of the electrolytes, yet has been rarely investigated. Herein, three anions of bis(trifluoromethanesulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI), and derived asymmetric (fluorosulfonyl)(trifluoro-methanesulfonyl)imide (FTFSI) are systematically examined in a weakly Li+ cation solvating solvent of bis(3-fluoropropyl)ether (BFPE). In-situ liquid secondary ion mass spectrometry demonstrates that FTFSI- and FSI- anions are associated with BFPE solvent, while weak TFSI-/BFPE cluster signals are detected. Molecular modeling further reveals that the anion-solvent interaction is accompanied by the formation of H-bonding-like interactions. Anion solvation enhances the Li+ cation transfer number and reduces the organic component in solid electrolyte interphase, which enhances the Li plating/stripping Coulombic efficiency at a low temperature of -30 degrees C from 42.4% in TFSI-based electrolytes to 98.7% in 1.5 m LiFTFSI and 97.9% in LiFSI-BFPE electrolytes. The anion-solvent interactions, especially asymmetric anion solvation also accelerate the Li+ desolvation kinetics. The 1.5 m LiFTFSI-BFPE electrolyte with strong anion-solvent interaction enables LiNi0.8Mn0.1Co0.1O2 (NMC811)||Li (20 mu m) full cell with stable cyclability even under -40 degrees C, retaining over 92% of initial capacity (115 mAh g-1, after 100 cycles). The anion-solvent interactions insights allow to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance. @@@ Anion solvation is demonstrated as a new direction to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance. The designed electrolyte with strong anion-solvent interaction enables 2.0 mAh cm-2 NMC811||Li (20 mu m) full cells to achieve excellent high voltage and low temperature performance, retaining over 92% of initial capacity after 100 cycles even under -40 degrees C.image
