Binary metal selenide nanowires wrapped over carbon fibers for a binder-free anode of sodium-ion batteries

Binary metal selenides (BMSs) have attracted considerable interest as potential anode materials for sodium-ion batteries (SIBs) due to significantly improved sodium storage performance resulting from higher intrinsic ionic conductivities and richer redox-active sites, particularly when compared to mono-metal selenides. In addition, the accumulation of binder in slurry preparation for electrodes not only accumulates dead weight but also diminishes the extent of the exposed surface area of active material. Henceforth, hierarchical nanostructures of nickel-cobalt selenide (NCSe) and iron-cobalt selenide (FCSe) bearing high surface area were deposited directly over carbon fibers and employed as free-standing anodes for SIBs (termed as NCSe/CFs and FCSe/CFs, respectively). A facile hydrothermal strategy, followed by optimized gas selenization was used to acquire hierarchical nanowire-like morphologies of BMSs on carbon fibers. Carbon fibers substrates not only provide current collecting pathways for electron transport during charging/discharging but also exhibit the high strength required for the free-standing electrode for battery assembly. When these electrodes were employed as an anode in SIBs, they exhibited adequately high initial energy capacities (i.e., 665 mA h g−1 by FCSe/CFs and 589 mA h g−1 by NCSe/CFs at 0.1 A g−1) and high-rate capabilities. Furthermore, these electrodes delivered outstanding stability in long-term cyclic performance over 1000 cycles at 1 A g−1. We believe that this simple strategy will further open a pathway toward the facile synthesis of numerous BMSs with carbon fiber composites as free-standing anodes for energy storage and conversion systems. [Display omitted] •Binary metal selenides (BMSs) coated carbon fiber composites as free-standing anodes for SIBs.•Hierarchical nanostructures of nickel-cobalt selenide (NCSe) and iron-cobalt selenide (FCSe).•Binder Free anode materials for SIBs.•Excellent Sodium storage performance of BMSs as free-standing anodes.•BMSs with outstanding rate capability and cyclic stability.