Bonding iron chalcogenides in a hierarchical structure for high-stability sodium storage

Owing to price-boom and low-reserve of Lithium ion batteries (LIBs), cost-cutting and well-stocked sodium ion batteries (SIBs) attract a lot of attention, aiming to develop an effective energy storage and conversion equipment. As a typical anode for SIBs, Iron sulfide (FeS) is difficult to maintain the high theoretical capacity. Structural instability and inherent low conductivity limit the cyclic and rate performance of FeS. Herein, hierarchical architecture of FeS-FeSe₂ coated with nitrogen-doped carbon (NC) is obtained by single-step solvothermal method and two-stage high-temperature treatments. Specifically, lattice imperfections provided by heterogeneous interfaces increase the Na⁺ storage sites and fasten ion/electron transfer. Synergistic effect induced by the hierarchical architecture effectively enhances the electrochemical activity and reduces the resistance, which contributes to the transfer kinetics of Na⁺. In addition, the phenomenon that heterogeneous interfaces provide more active site and extra migration Na⁺ path is also proved by density functional theory (DFT). As an anode for SIBs, FeS-FeSe₂/NC (FSSe/C) delivers highly reversible capacity (704.5 mAh·g^-1 after 120 cycles at 0.2 A·g^-1), excellent rate performance (326.3 mAh·g^-1 at 12 A·g^-1) and long-lasting durability (492.3 mAh·g^-1 after 1000 cycles at 4 A·g^-1 with 100 % capacity retention). Notably, the full battery, assembled with FSSe/C and Na₃V₂(PO₄)₃/C (NVP/C), delivers reversible capacity of 252.1 mAh·g^-1 after 300 cycles at 1 A·g^-1. This work provides a facile method to construct a hierarchical architecture anode for high-performance SIBs.