Urchin-Like Fe₃ Se₄ Hierarchitectures: A Novel Pseudocapacitive Sodium-Ion Storage Anode with Prominent Rate and Cycling Properties

Transition metal chalcogenides have received great attention as promising anode candidates for sodium-ion batteries (SIBs). However, the undesirable cyclic life and inferior rate capability still restrict their practical applications. The design of micro-nano hierarchitectures is considered as a possible strategy to facilitate the electrochemical reaction kinetics and strengthen the electrode structure stability upon repeated Na⁺ insertion/extraction. Herein, urchin-like Fe₃ Se₄ hierarchitectures are successfully prepared and developed as a novel anode material for SIBs. Impressively, the as-prepared urchin-like Fe₃ Se₄ can present an ultrahigh rate capacity of 200.2 mAh g^-1 at 30 A g^-1 and a prominent capacity retention of 99.9% over 1000 cycles at 1 A g^-1 , meanwhile, a respectable initial coulombic efficiency of ≈100% is achieved. Through the conjunct study of in situ X-ray diffraction, ex situ X-ray absorption near-edge structure spectroscopy, as well as cyclic voltammetry curves, it is intriguing to reveal that the phase transformation from monoclinic to amorphous structure accompanied by the pseudocapacitive Na⁺ storage behavior accounts for the superior electrochemical performance. When paired with the Na₃ V₂ (PO₄ )₃ cathode materials, the assembled full cell enables high energy density and decent cyclic stability, demonstrating potential practical feasibility of the present urchin-like Fe₃ Se₄ anode.