A BF3-Doped MXene Dual-Layer Interphase for Reliable Lithium Metal Anode

Abstract

The surface modification of lithium metal anode poses a promising way in reaching high energy-density batteries. Here we introduce a dual-layer interphase that consists of an in-situ formed lithium carboxylate organic layer and an ultra-thin BF3-doped monolayer Ti3C2 MXene on Li metal surface (Shang, Shovon, Wong, Niu. Advanced Materials, 35 (2023) 2210111). The honeycomb-structured organic layer increases the wetting of electrolyte due to the large surface area, leading to a thin solid electrolyte interface (SEI). While the BF3-doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic-rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells was received. The functional BF3 groups along with the excellent electronic conductivity and smooth surface of the MXene greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite-free lithium metal anode. The battery paired with NMC811 exhibited a high initial Coulombic efficiency (CE) of 82.1%. A high capacity-retention of 175.4 mAh/g at 1.0 C was achieved after 350 cycles. After long 500 cycles, a reliable capacity was still remained while the cell with un-modified Li metal quickly dropped to below 74.2 mAh/g. In a pouch cell with a capacity of 475 mAh, the battery still exhibited a high discharge capacity of 165.6 mAh/g with a capacity retention of 90.2% after 200 cycles, while the cell with pure Li metal decreased to 80.5%. Keywords: Lithium metal electrode; Lithium ion battery; MXene; Doping