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Composition Engineering Boosts Voltage Windows for Advanced Sodium Ion Batteries.

Transition metal selenides have captured sustainable research attention in energy storage and conversion field as promising anodes for sodium-ion batteries. However, for the majority of transition metal selenides, the potential windows have to compress to 0.5-3.0 V for the maintenance of cycling and rate capability, which largely sacrifices the capacity under low voltage and impair energy density for sodium full batteries. Herein, through introducing diverse metal ions, transition metal selenides consisted of different compositions doping (CoM-Se2@NC, M=Ni, Cu, Zn) are prepared with more stable structures and higher conductivity, which exhibit superior cycling and rate properties than those of CoSe2@NC even at a wider voltage range for sodium ion batteries (SIBs). Particularly, Zn2+ doping demonstrates the most prominent sodium storage performance among series materials, delivering high capacity of 474 mAh g-1 after eighty cycles at 500 mA g-1 and rate capacities of 511.4, 382.7, 372.1, 339.2, 306.8 and 291.4 mAh g-1 at current densities of 0.1, 0.5, 1.0, 1.4, 1.8 and 2.0 A g-1, respectively. The composition adjusting strategy based on metal ions doping can optimize electrochemical performances of metal selenides, offer an avenue to expand stable voltage windows and provide a feasible approach for the construction of high specific energy sodium ion batteries.