Solvation-Heterostructure Synergy Enables Reversible Four-Electron Conversion in High-Capacity Na-Ion Electrodes

The practical deployment of high-capacity conversion-type electrode materials in Na-ion storage remains constrained by insufficient reaction kinetics and irreversible phase transitions. While extensive efforts have focused on optimizing the intrinsic structural stability and redox activity of electrode materials, the critical role of electrolyte solvation chemistry in mediating phase evolution dynamics has been underexplored. Herein, we propose a solvation engineering strategy utilizing dimethoxyethane (DME)-based electrolytes to enable kinetically favorable and fully reversible phase transitions in conversion-type MoSe₂. We systematically reveal that the tailored Na⁺-2DME solvation structure eliminates energy-intensive desolvation barriers, facilitating direct co-intercalation of solvated Na⁺ species into the MoSe₂ lattice. This mechanism not only accelerates interfacial charge transfer but also mitigates parasitic electrolyte decomposition. Moreover, the solvation-induced lattice expansion of MoSe₂ alleviates mechanical strain during repeated cycling, ensuring structural integrity and maintaining rapid ion diffusion pathways. Crucially, the solvation-assisted reaction pathway unlocks a four-electron transfer process of the double-heterostructures MoSe₂-TiO₂-MXene (MTM) anode, achieving complete conversion to Na₂Se and Mo during sodiation, followed by near-theoretical regeneration of MoSe₂ upon desodiation. This study establishes a mechanistic framework for leveraging solvent-specific solvation effects to regulate phase transition thermodynamics and kinetics in conversion-type electrodes, offering universal design principles for high-performance Na-ion storage devices.