Novel pseudo-crown ether-like lithium salt enabling fast charging/discharging high-energy lithium metal batteries

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Abstract Conventional carbonate-based electrolytes defected all racers and became a dominant leader in the lithium-ion battery industry due to superior overall performance of preferable physical, chemical and electrochemical properties. However, carbonate-based electrolytes with high corrosion towards lithium (Li) metal result in massive dendrites growth and limited cycling life, thereby blocking their application in Li metal batteries (LMBs). This is particularly true for practical LMBs with high areal capacity (> 3.5 mAh/cm2), which generally requires a high areal current density (> 1 mA/cm2) for an acceptable, realistic charging rate. Herein, we design an asymmetric functional lithium salt, lithium 1,1,1-trifluoro-N-[2-[2-(2-methoxy ethoxy)ethoxy)]ethyl] methanesulfonamide (LiFEA) that enables carbonate electrolytes with a large apparent donor number and transference number, thus leading to excellent compatibility with Li metal anodes even at high current densities. The unique pseudo-crown ether-like, folded molecular geometry endows its novel post-“self-cleaning” mechanism: the LiFEA could dissolve most undesirable organic species in the initial deposited solid electrolyte interphase (SEI) layer and gradually enrich the inorganic species. This self-cleaning behavior of LiFEA results in homogeneous and more inorganic-rich, ultrathin SEI layers (which also contributes to high-quality cathode electrolyte interphase) and, therefore, outstanding lithium metal battery performances. Advanced LiFEA-based carbonate electrolytes could achieve high-performance cyclability and fast charging/discharging performances for LMBs. Li||NCM811 half cells enabled 500 cycles with an 83.5% capacity retention for 5 C-cycling (i.e., 3 mA/cm2), and full cells allowed 100 cycles with 86.5% capacity retention for cycling under the high current density of 5.2 mA/cm2 (i.e., 2 C). Under realistic conditions, industrial Li||NCM811 metal pouch cells achieve ~ 310 Wh/kg (except taps and packing foil, 403 Wh/kg) for a cell-level energy density, enabling stable cycling up to 100 cycles under a high discharging current density of 3.66 mA/cm2 (i.e., 1 C) and yielding a record-high power density of ~ 408 W/kg (except taps and packing foil, 530 W/kg). Our designed functional lithium salt with a special molecular geometry for carbonate-based electrolytes enables a promising path to realistic LMBs with high energy and high discharging power densities.

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