Engineering the solvent-anion interactions of LiTFSI-based dual-salt electrolytes to sustain high-performance NCM622 cathodes

Abstract

Electrolytes play a vital role in determining the performances of lithium-ion batteries (LIBs), especially the high-voltage LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode in LiTFSI-based electrolytes. Herein, we report a high-capacity and stable NCM622 cathode that can be realized in LiTFSI-based (named T) carbonate electrolytes by tuning the intermolecular interactions using the added LiDFOB (named D). In the 1 M dual-salt electrolyte, the cathode failure and Al corrosion are suppressed in the 4.5 V-NCM622||Li batteries, because a uniform interfacial layer and weaker Li⁺-solvent interactions are built to inhibit the parasitic reactions. As a result, the capacity retention reaches 94.68% after 200 cycles and the 10 C-rate capacity is about 160 mA h g^-1 in the 1 M T + D dual-salt electrolyte. Unlike the commonly used electrolyte, the FEC additive increases the de-solvation barrier and disturbs the cycle stability in (T + D) dual-salt systems. Density functional theory (DFT) calculation and nuclear magnetic resonance (NMR) spectra reveal that the additive FEC changes the solvent-solvent and solvent-anion interactions in the presence of T + D, which weakens the electrolyte-cathode compatibility. This work indicates that regulating the solvation structure and interfacial chemistry from solvent-solvent/anion interactions is promising for designing high-performance LIBs by using dual‐salt electrolytes.