Active-Site-Switching in Medium-Entropy Metal Sulfides for Wide-Temperature High-Power Zn-Air Pouch Cells.

Abstract

Quasi-solid-state Zn-air pouch cells (QZPCs) promise a high energy-to-cost ratio while ensuring inherent safety. However, addressing the challenges associated with exploring superior energy-wise cathode catalysts along with their activity origin, and the super-ionic electrolytes remains a fundamental task. Herein, the realistic high-performance QZPCs are contrived, underpinned by a robust NiVFeCo medium-entropy metal sulfides (MESs) bifunctional air cathode with a record-low potential polarization of 0.523 V, paired with a sodium polyacrylate-ionic liquid hydrogel exhibiting exceptional conductivity (234 mS cm^-1) and water retention (93.8% at 7 days) at room temperature as the super-ionic conductor electrolyte. Through combined studies of in situ Raman, ex situ X-ray absorption fine structure analysis, and theoretic calculations, an intriguing adaptive active-sites-switching mechanism of the MESs cathode during discharging/charging processes is unveiled, revealing a dynamic role transition of Co and Ni active sites in the reversible oxygen electrocatalysis. Consequently, the persistent low cathode polarization and super ion-conductive electrolyte endorse QZPCs an excellent rate performance from 1 to 100 mA cm^-2 at room temperature. Moreover, an impressively high cell-level energy density of 105 Wh kg_cell ^-1 with an ultra-long cycle lifespan of 4000 cycles at 5 mA cm^-2 and a low temperature of -30 °C is achieved.