Molecular Intercalation Enables Phase Transition of MoSe₂ for Durable Na-Ion Storage

1T-MoSe₂ is recognized as a promising anode material for sodium-ion batteries, thanks to its excellent electrical conductivity and large interlayer distance. However, its inherent thermodynamic instability often presents unparalleled challenges in phase control and stabilization. Here, a molecular intercalation strategy is developed to synthesize thermally stable 1T-rich MoSe₂, covalently bonded to an intercalated carbon layer (1T_R/2H-MoSe₂@C). Density functional theory calculations uncover that the introduced ethylene glycol molecules not only serve as electron donors, inducing a reorganization of Mo 4d orbitals, but also as sacrificial guest materials that generate a conductive carbon layer. Furthermore, the C─Se/C─O─Mo bonds encourage strong interfacial electronic coupling, and the carbon layer prevents the restacking of MoSe₂, regulating the maximum 1T phase to an impressive 80.3%. Consequently, the 1T_R/2H-MoSe₂@C exhibits an extraordinary rate capacity of 326 mAh g^-1 at 5 A g^-1 and maintains a long-term cycle stability up to 1500 cycles, with a capacity of 365 mAh g^-1 at 2 A g^-1. Additionally, the full cell delivers an appealing energy output of 194 Wh kg^-1 at 208 W kg^-1, with a capacity retention of 87.3% over 200 cycles. These findings contribute valuable insights toward the development of innovative transition metal dichalcogenides for next-generation energy storage technologies.