MXenes hold significant potential in lithium-sulfur (Li-S) battery applications due to its robust polysulfide adsorption and catalytic effect on polysulfide transformation achieved by adjustable transition metals and surface functional groups. Introduction of heteroatoms can prompt an electron distribution and refine MXenes surface structure, thereby substantially enhancing its electrochemical capabilities. Herein, partially oxidized Ti_3-yNb_yC₂T_x (O-Ti_3-yNb_yC₂T_x) heterostructure has been prepared by in-situ oxidization of Ti_3-yNb_yC₂T_x MXene in anhydrous ethanol. The incorporation of niobium (Nb) species within the Ti₃C₂T_x matrix plays a pivotal role: augmenting the catalytic conversion of polysulfides and concurrently fortifying the cyclic stability of the electrode constituents. When employed in Li-S batteries separator and cathode, it delivers impressive rate performance and durability. The O-Ti_2.7Nb_0.3C₂T_x/S cathode exhibits an initial discharge capacity of 1260 mA·h/g at a current density of 0.1 C, and a minuscule capacity decay rate of a mere 0.029% per cycle over 2000 cycles at 1C. Even at a significantly elevated current density of 4 C, an appreciable capacity of 640 mA·h/g is sustained. This research opens new avenues to explore MXene heterostructures with both superior electrocatalytic and adsorption properties for alkali metal-S batteries.

Contradiction between ultrafast nucleation and deposition rates of lithium (Li) crystals at high rate and heterogeneity of Li⁺ flux resulting from concentration polarization has compromised the performance of Li metal anodes especially at high areal capacity and current density. Here, multifunctional protective layer consisting of MoO₃ nanobelt films (MoO₃-NF) is introduced on the surface of Li by a simple rolling method. The strong binding energy between Li and MoO₃ guides the homogeneous nucleation and deposition of Li, while the nanobelt networks provide effective ion channels for uniform distribution of the Li⁺ flux. Because of the novel multifunctional protective layer, the MoO₃-NF@Li anodes demonstrate a remarkable stability for 800 h with ultralow overpotential of 159 mV at extreme harsh conditions of 60 mA·h/cm² and 60 mA/cm². MoO₃-NF@Li||LiNi_0.6Co_0.2Mn_0.2O₂ full-cells can run 100 cycles with a superior capacity retention of 84.2% under practical test conditions, demonstrating great potential for high output and energy-density metal batteries.