Free-standing medium-entropy porous needle-like FeCoCuNi phosphide nanowires-formed flower clusters/carbon fiber anode with high capacity and long durability for sodium-ion batteries

The drastic volume expansion and slow sodium-ion kinetics hinder the practical application of phosphides with high specific capacity and low discharge voltage in sodium-ion batteries (SIBs). Herein, we introduced entropy configuration into nanostructures and prepared a novel free-standing, three-dimensional, porous needle-like medium-entropy Fe, Co, Cu, Ni phosphide (ME-FCCNP) nanowires-formed flower clusters/carbon fiber cloth (CFC) anode (ME-FCCNP@CFC) for SIBs. The distorted lattices caused by medium-entropy configuration provide abundant sites for sodium-ion reactions and improve the electron transfer rate. The medium-entropy effects improve the mechanical stability, while the three-dimensional networks and porous needle-like nanowires provide sufficient space for the volume expansion. These combined properties enable the ME-FCCNP@CFC electrode to exhibit a high-rate capability of 170.8 mAh g−1 at 5.0 A g−1 and deliver a specific capacity of 325.8 mAh g−1 after 2000 cycles at 2.0 A g−1, far surpassing most of reported transition-metal phosphides. Moreover, the Na3V2(PO4)3 || ME-FCCNP@CFC full cell showcases a high-energy density of 256.8 Wh kg−1 and a long cycling life (267.8 mAh g−1 at 2.0 A g−1 with a capacity retention of 83.2 % after 1000 cycles). These results provide significantly promising implications for the anode design of SIBs by employing self-supporting and medium-entropy structures. One novel free-standing three-dimensional medium-entropy porous needle-like iron, cobalt, copper, nickel phosphide (ME-FCCNP) nanowires-formed flower clusters/carbon fiber cloth (CFC) anode (ME-FCCNP@CFC) for sodium-ion batteries is fabricated by simple hydrothermal and phosphorization process. The ME-FCCNP@CFC delivers a high rate capability of 170.8 mAh g−1 at 5 A g−1 and a specific capacity of 325.8 mAh g−1 after 2000 cycles at 2 A g−1. Moreover, the Na3V2(PO4)3 || ME-FeCoCuNiP@CFC full cell shows a high energy density of 256.8 Wh kg−1 and long-term stability. [Display omitted] •A novel free-standing medium-entropy FeCoCuNi phosphide composite anode is prepared.•The obtained anode exhibits high capacity, rate capability and long durability.•Unique morphology and medium-entropy structure enhance the capacity and stability.•Assembled full battery shows a high energy density of 256.8 Wh kg−1 and long cycle.