Highly stabilized FeS2 cathode design and energy storage mechanism study for advanced aqueous FeS2–Cu battery

Aqueous batteries exhibite great potential for large-sacle energy storage due to their intrinsic safety, eco-friendliness, and low cost. However, the inadequate capacity and poor cycling stability impede the futher development. Herein, FeS2 compounded with three-dimensional carbon fibers are designed as the self-supporting cathodes in aqueous copper ion system, where the microporous/mesoporous (within 10 nm) are proposed to improve the rapid electron transfer and strengthen the electrolyte wettability. The results reveal that FeS2@CNFs700 exhibits a specific capacity of 462 mAh g−1 after 1600 cycles at 5 A g−1 with low capacity degradation of only 0.022 % and 385 mAh g−1 after 4000 cycles with high coulombic efficiency of 97.5 %, prossessing superior rate performance (387 mAh g−1 at 15 A g−1). Furthermore, the reversible reaction pathway of FeS2 → CuS → Cu7S4 → Cu2S is demonstrated by a series of ex-situ testing, proving the feasibility of FeS2 in aqueous batteries at ambient temperature. In addition, the assembled Zn//FeS2@CNFs hybrid battery exhibits a stable reversible specific capacity of 510 mAh g−1 and a specific energy of 459 Wh kg−1 at 1 A g−1 with an excellent cycling stability (capacity decay: 2.77 % after 50 cycles). This work offers unique insights about stable FeS2-aqueous batteries designing. [Display omitted] •Self-supporting cathode is designed by electrostatic spinning.•Microporous (within 10 nm) can efficiently improve the rapid electron transfer.•FeS2@CNFs demonstrates excellent stability during long cycle test at 5 A/g.•The reversible reaction pathway of FeS2 .→ CuS → Cu7S4 → Cu2S is proved in FeS2//Cu battery.•Hybrid battery of FeS2//Zn is designed to improve the operational voltage.