Bidirectional Atomic Iron Catalysis of Sulfur Redox Conversion in High‐Energy Flexible ZnS Battery

Abstract

To achieve the full theoretical potential of high energy ZnS electrochemistry, the incomplete and sluggish conversion during battery discharging and high reactivation energy barrier during battery recharging associated with the sulfur cathodes must be overcome. Herein, the atomically dispersed Fe sites with FeN 4 coordination are experimentally and theoretically predicted as bidirectional electrocatalytic hotspots to simultaneously manipulate the complete sulfur conversion and minimize the energy barrier of ZnS decomposition. It is discovered that the Fe sites were favorable for strong sulfur and possible zinc polysulfide intermediate adsorption, and ensure nearly complete sulfur to ZnS conversion during discharge. For the following recharging process, the electrodeposited ZnS can be readily reversible charged back to S without a noticeable activation overpotential around FeN 4 moieties comparing to pure carbon matrixes. As expected, the freestanding iron embedded carbon fiber cloth supported sulfur cathode delivers a high specific capacity of 1143 mAh g −1 and a lower voltage hysteresis of 0.61 V. As elaborated by postmortem analysis, the degradation mechanism of ZnS cell is the accumulation of inactive ZnS crystals on the cathode side rather than the Zn metallic depletion. More encouragingly, a flexible solid-state ZnS battery with a high discharge capacity and stable reversibility is also demonstrated.

Minireview on Aqueous Zinc–Sulfur Batteries: Recent Advances and Future Perspectives

“…The peaks of S 8 vanished, and just one pair of ZnS peaks was seen when the electrode was discharged to 0.1 V (point C), confirming that the ultimate discharge product is ZnS. The peaks of S 8 progressively appeared throughout the recharging process (points D–F), showing the reversible conversion between S 8 and ZnS . In contrast to the one-step conversion reaction of S to ZnS observed in an aqueous electrolyte, the reaction mechanism in the hybrid electrolyte involves a multistep conversion reaction between S and ZnS.…”

“…The peaks of S 8 progressively appeared throughout the recharging process (points D−F), showing the reversible conversion between S 8 and ZnS. 54 In contrast to the one-step conversion reaction of S to ZnS observed in an aqueous electrolyte, the reaction mechanism in the hybrid electrolyte involves a multistep conversion reaction between S and ZnS. The Raman spectra of the discharging state c, as depicted in Figure 14a, reveal the presence of three distinct peaks at 317, 420, and 610 cm −1 .…”

“…The redox-mediated chemical conversion enables the cell to exhibit a high reversible discharge capacity of 1205 mAh g –1 at 0.1 A g –1 with an operating voltage of 0.58 V (Figure b). In parallel work, Zhang et al proposed another technique to simultaneously deal with the kinetic challenges during charge and discharge . They devised bidirectional catalytic sites via the implantation of single iron atoms in nitrogen-doped porous carbon frameworks (Figure c).…”

“…(c) Representation of the synthesis process of a polymer-coated freestanding sulfur cathode (S@FeNC/NC/CC). This panel was reproduced with permission from ref . Copyright 2023 Wiley.…”

“…(d) XPS spectra of the sulfur cathode at different points are shown in the typical voltage profile (left side) of the Zn–S cell during charging and discharging. This panel was reproduced with permission from ref . Copyright 2023 Wiley.…”