MXene-Based Composite Anodes for Sodium-Ion Batteries: Material Design, Storage Mechanisms, and Practical Challenges

MXenes have attracted considerable attention as anode materials for sodium-ion batteries (SIBs) because of their metallic conductivity, hydrophilic surfaces, tunable surface terminations, and layered structures. However, pristine MXenes are limited by nanosheet restacking, oxidation instability, heterogeneous surface chemistry, low initial Coulombic efficiency, and insufficient electrode-level ion accessibility. These issues indicate that MXenes should be regarded not simply as standalone active materials but as multifunctional building blocks for composite electrode design. This review discusses recent progress in MXene-based composite anodes for SIBs, focusing on MXene/carbon composites, MXene/metal compound composites, polymer-assisted composites, and three-dimensional structured MXene composites for improving structural stability, interfacial chemistry, and sodium-storage kinetics. We emphasize that composite engineering can reshape sodium storage from diffusion-limited intercalation toward hybrid mechanisms involving interfacial adsorption, pseudocapacitive storage, heterointerface-driven redox reactions, ion desolvation regulation, and solid-electrolyte interphase stabilization. Key practical challenges, including oxidation control, initial Coulombic efficiency, high-mass-loading electrode design, gravimetric–volumetric performance trade-offs, scalable synthesis, and full-cell validation, are also discussed. Finally, we propose future design principles based on integrated materials chemistry, interfacial science, multiscale architecture engineering, and realistic cell-level evaluation for advancing MXene composites toward practical SIB anodes.