Topochemical transformation has emerged as a promising method for fabricating two-dimensional (2D) materials with precise control over their composition and morphology. However, the large-scale synthesis of ultrathin 2D materials with controllable thickness remains a tremendous challenge. Herein, we adopt an efficient topochemical synthesis strategy, employing a confined reaction space to fabricate ultrathin 2D Sn₄P₃ nanosheets in large-scale. By carefully adjusting the rolling number during the processing of Sn/Al foils, we have successfully fabricated Sn₄P₃ nanosheets with varied layer thicknesses, achieving a remarkable minimum thickness of two layers (~ 2.2 nm). Remarkably, the bilayer Sn₄P₃ nanosheets display an exceptional initial capacity of 1088 mAh·g⁻¹, nearing the theoretical value of 1230 mAh·g⁻¹. Furthermore, we reveal their high-rate property as well as outstanding cyclic stability, maintaining capacity without fading more than 3000 cycles. By precisely controlling the layer thickness and ensuring nanoscale uniformity, we enhance the lithium cycling performance of Sn₄P₃, marking a significant advancement in developing high-performance energy storage systems.

Lithium-sulfur (Li-S) batteries mainly rely on the reversible electrochemical reaction of between lithium ions (Li⁺) and sulfur species to achieve energy storage and conversion, therefore, increasing the number of free Li⁺ and improving the Li⁺ diffusion kinetics will effectively enhance the cell performance. Here, Mo-based MXene heterostructure (MoS₂@Mo₂C) was developed by partial vulcanization of Mo₂C MXene, in which the introduction of similar valence S into Mo-based MXene (Mo₂C) can create an electron delocalization effect. Through theoretical simulations and electrochemical characterisation, it is demonstrated that the MoS₂@Mo₂C heterojunction can effectively promote ion desolvation, increase the amount of free Li⁺, and accelerate Li⁺ transport for more efficient polysulfide conversion. In addition, the MoS₂@Mo₂C material is also capable of accelerating the oxidation and reduction of polysulfides through its sufficient defects and vacancies to further enhance the catalytic efficiency. Consequently, the Li-S battery with the designed MoS₂@Mo₂C electrocatalyst performed for 500 cycles at 1 C and still maintained the ideal capacity (664.7 mAh·g⁻¹), and excellent rate performance (567.6 mAh·g⁻¹ at 5 C). Under the extreme conditions of high loading, the cell maintained an excellent capacity of 775.6 mAh·g⁻¹ after 100 cycles. It also retained 838.4 mAh·g⁻¹ for 70 cycles at a low temperature of 0 °C, and demonstrated a low decay rate (0.063%). These results indicate that the delocalized electrons effectively accelerate the catalytic conversion of lithium polysulfide, which is more practical for enhancing the behaviour of Li-S batteries.

High energy density and low cost make lithium-sulfur (Li-S) batteries as one of the next generation's promising energy storage systems. However, the following problems need to be solved before commercialization: (i) the shuttling effect and sluggish redox kinetics of lithium polysulfides in sulfur cathode; (ii) the formation of lithium dendrites and the crack of solid electrolyte interphase; (iii) the large volume changes during charge and discharge processes. MXenes, as newly emerging two-dimensional transition metal carbides/nitrides/carbonitrides, have attracted widespread attention due to their abundant active surface terminals, adjustable vacancies, and high electrical conductivity. Designing MXene-based heterogeneous structures is expected to solve the stacking problem induced by hydrogen bonds or Van der Waals force and to provide other charming physiochemical properties. Herein, we generalize the design principles of MXene-based heterostructures and their functions, i.e., adsorption and catalysis in advanced conversion-based Li-S batteries. Firstly, the physiochemical properties of MXene and MXene-based heterostructures are briefly introduced. Secondly, the catalytic functions of MXene-based heterostructures with the compositional constituents including carbon materials, metal compounds, organic frameworks, polymers, single atoms and special high-entropy MXenes are comprehensively summarized in sulfur cathodes and lithium anodes. Finally, the challenges of MXene-based heterostructure in current Li-S batteries are pointed out and we also provide some enlightenments for future developments in high-energy-density Li-S batteries.