Reformulating Carbonate Electrolyte for Ultrastable Lithium Metal Anode via Anion Receptors

The lithium metal anode has been regarded as one of the best anodes due to its ultrahigh specific capacity (3860 mAh·g–1), low density (0.59 g·cm–3), and low redox potential (−3.04 V vs the standard hydrogen electrode). However, its practical implementation is hindered by the low columbic efficiency (CE) and safety issues. Lithium nitrate (LiNO3) has been widely proven as an effective additive to tackle the issue, but very limited solubility in carbonate solvents makes it difficult to be introduced into current commercial electrolytes. Herein, cost-effective AlCl3 is proposed as the anion receptor to promote the dissolution of LiNO3 in carbonate electrolytes, and the underlying mechanism is investigated via Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The optimized AlCl3 + LiNO3 + fluoroethylene carbonate (FEC)-containing electrolyte was used in Li|Cu and Li|LiFePO4(LFP) cells, and it induced significant improvement in cycling stability and polarization suppression. The effectiveness of the designed electrolyte was further confirmed in a practical Li|LFP cell with a thin Li anode and limited electrolyte. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) reveal that the introduced AlCl3 and LiNO3 can help in inorganic-rich solid electrolyte interface (SEI) formation and compact Li deposition, and these benefits contribute to the enhanced cycling stability.