Single-atom-engineered MXene heterostructures: Synthesis strategies and mechanistic insights for Lithium-, sodium-, potassium-, zinc-, sulfur-, and supercapacitor-based energy storage.

Single-atom-doped MXenes (SADMs) are developing as a promising category of two-dimensional materials with significant prospects to enhance battery technologies, including lithium-based systems and others. Researchers have attained significant enhancements in electrochemical performance by integrating the inherent characteristics of MXenes, including excellent electrical conductivity, adjustable surface terminations, and exceptional mechanical strength, with the atomic-level modulation facilitated by single-atom dopants. This paper comprehensively outlines current advancements in synthetic methodologies for integrating isolated metal atoms into MXene frameworks and developing MXene-based heterostructures for enhanced performance in lithium and beyond lithium batteries technology. A range of synthesis methods, such as in situ doping during MXene etching, post-synthetic wet-chemical modification, atomic layer deposition, electrochemical deposition, and thermal treatment are rigorously analyzed, focusing on the regulation of dopant distribution, coordination environment, electronic structure, and long-term stability. We emphasize the synergistic effects of single-atom doping strategy enhance critical battery parameters, including diffusion kinetics, specific capacity, rate capability, structural integrity, and cycling stability for lithium-ion batteries, lithium-metal batteries, lithium‑sulfur batteries, sodium-ion batteries, zinc-ion batteries and supercapacitors. Additionally, issues concerning dopant migration, synthesis scalability, surface oxidation, and interfacial compatibility are examined, along with prospective potential for device-level applications. Finally, the challenges and potential prospects of SADMs in energy storage are examined. Through continuous research and development, SADMs are positioned to transform the sector, acting as fundamental components in the shift toward sustainable and clean energy. This review seeks to elucidate the design ideas and synthesis advancements driving SADMs toward next-generation, high-efficiency lithium and beyond lithium energy storage devices.