Bidirectional Atomic Iron Catalysis of Sulfur Redox Conversion in High‐Energy Flexible ZnS Battery

Abstract

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.