Defect-interface synergistic engineering of Bi 2 Te 3– x @MXene anodes toward fast-charging and durable sodium storage

Metal tellurides are promising anode candidates for high-energy sodium-ion batteries (SIBs) owing to their multielectron redox chemistry, but their practical deployment is limited by sluggish reaction kinetics and severe structural instability associated with repeated conversion/alloying reactions. Herein, a Te-vacancy-rich Bi2Te3-x@MXene heterostructure is rationally constructed via synergistic electrostatic assembly and in situ tellurization. Strong Ti-Te interfacial coupling immobilizes Bi2Te3-x nanoparticles on conductive MXene nanosheets, generating a robust three-dimensional architecture with continuous electron/ion transport pathways and enhanced tolerance to volume variation. Meanwhile, Te-vacancy engineering tailors the electronic structure and creates abundant active sites, synergistically accelerating Na⁺ transport kinetics. Combined electrochemical analysis and in situ/ex situ characterizations reveal a highly reversible insertion-conversion-alloying mechanism with stabilized phase evolution during cycling. Consequently, the Bi2Te3-x@MXene anode delivers outstanding rate capability and ultralong cycling stability, retaining 324.8 mAh g-1 after 2000 cycles at 2 A g-1 and maintaining 317.9 mAh g-1 even at 10 A g-1. Moreover, the Na3V2(PO4)3//Bi2Te3-x@MXene full cell achieves a high energy density of 210.6 Wh kg-1 and preserves 104.7 Wh kg-1 even at an ultrahigh power density of 11300 W kg-1. This work highlights the effectiveness of integrating defect chemistry with heterointerface engineering to unlock fast and durable sodium storage in metal tellurides for high-energy and high-power SIBs.