A Hydrophobic and High Surface Charge Phosphate Interphase for High Areal Capacity Zinc Metal Batteries

Abstract

Commercial zinc metal batteries require an areal capacity above 4 mAh cm⁻² at high rates. However, such performance is rarely reported due to slow mass transport between the diffuse layer and the outer Helmholtz layer at the interface. Herein, it is reported an unprecedented Sand's capacity exceeding 64 mAh cm⁻² at 20 mA cm⁻², enabled by a hydrophobic and high surface charge iron/zinc phosphate (FZP) nanofilm serving as an artificial solid electrolyte interphase for zinc anode. It is identified the key role of high surface charge with strong Zn²⁺ affinity, which mitigates depletion zones by forming a narrower and Zn²⁺-rich electric double layer, thereby achieving high areal capacities and promoting preferential exposure of the Zn (100) plane. Consequently, FZP/Zn exhibits stable cycling for 400 h under 60% depth-of-discharge (2.14 mAh cm⁻²). Full cells with a low N/P ratio deliver an energy density of 176.5 Wh kg⁻¹ _electrodes at 6 mAh cm⁻². The practical Zn-I₂ pouch cells are further demonstrated with ≈97 Ah of cumulative capacity and a high areal capacity of 5.12 mAh cm⁻². These findings establish FZP nanofilms as a viable strategy for realizing commercial high-areal-capacity aqueous zinc-ion batteries.