Metal–organic framework derived bimetallic selenide embedded in nitrogen-doped carbon hierarchical nanosphere for highly reversible sodium-ion storage

Bimetallic selenides with various valence transitions and high theoretical capacities are extensively studied as anodes for sodium-ion-batteries (SIBs), but their huge volume changes and poor capacity retention limit their practicality. Herein, a facile and controllable strategy using a binary Ni-Co metal–organic framework (MOF) precursors followed by the selenization process, which produced a cobalt nickel selenide/ N -doped carbon composite ((CoNi)Se 2 /NC) that maintained the hierarchical nanospheres structure. Such a distinctive structure affords both Na + and electron diffusion pathways in the electrochemical reactions as well as high electrical conductivity, thus leading to superior electrochemical performance when the designed composite is utilized as an anode in SIBs. The resulting nanospheres-like (CoNi)Se 2 /NC hierarchical structure exhibits a high specific capacity of 526.8 mA h g −1 at 0.2 A/g over 100 cycles, a stable cycle life with no obvious capacities loss at 1.0 and 3.0 A/g after 500 cycles, and exceptional rate capability of 322.9 mA h g −1 at 10.0 A/g.