Boosting High Energy Density Lithium-Ion Storage via the Rational Design of an FeS-Incorporated Sulfurized Polyacrylonitrile Fiber Hybrid Cathode

In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g_{(FeS@SPAN composite)}^-1 at the end of 500 cycles at 1 A g^-1 even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg_{(FeS@SPAN composite)}^-1, much higher than the theoretical energy density of the commercial LiCoO₂ cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.