Concentrated precipitation electrolyte for reviving ultrathin lithium metal anode

Realizing high-performance lithium metal batteries requires the presence of a robust solid-electrolyte interphase (SEI) on the Li metal surface that forms before or during operation. Herein, high concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrite (LiNO3) are employed to create a novel concentrated precipitation electrolyte (CPE) and form an inorganic-rich SEI. It is found that an ultrathin Li metal anode (thickness of 25 μ m) in the CPE remains highly reversible over 300 cycles with an average Coulombic efficiency (CE) of 97.21 % in an asymmetric Cu|Li cell. The CPE enables superior stability to the LiFePO4 (LFP) cathode at a high mass loading of ∼15 mg cm−2 and reaches a capacity retention of 82.8 % after 100 cycles with an average CE of 99.94 %. This study elucidates the mechanism of LiTFSI and LiNO3 in enhancing the physiochemical properties of the SEI surface layer. It is believed that this design concept and the findings can be broadened to optimize SEIs via electrolyte engineering for practical Li metal batteries.