A BF 3 -Doped MXene Dual-Layer Interphase for Reliable Lithium Metal Anode.

To maintain a reliable lithium deposition and extraction on lithium metal anode during charging/discharging, surface modification poses a promising way in reaching high energy-density batteries. We report a dual-layer interphase that consists of an in-situ formed lithium carboxylate organic layer and an ultra-thin BF 3 -doped monolayer Ti 3 C 2 MXene on Li metal surface. 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 BF 3 -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 BF 3 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 with the dual-layer coated lithium metal (D-Li) as anode displayed greatly improved electrochemical performance. 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%. In contrast to the fast capacity decay of pure Li metal, the battery using NCA as cathode also displayed excellent capacity retention in both coin and pouch cells. The BF 3 -doped 2D MXene dual-layer modified surface provides an effective approach in stabilizing Li metal anode in rapidly growing large energy-density batteries. This article is protected by copyright. All rights reserved.