Taming Zn Electrochemistry with Carbon Nitride: Atomically Gradient Interphase for Highly Reversible Aqueous Zn Batteries

The irreversibility issuesof metallic zinc (Zn) anode of low Coulombic efficiency, persistent parasitic reactions, and severe dendrite growth remain a fundamental, century-old challenge hindering the practical applications in rechargeable aqueous batteries. Herein, a promising atomically gradient solid electrolyte interphase (SEI) strategy is demmonstrated, in which the bottom sublayer of atomic Cu dispersed carbon nitride tightly anchors the whole SEI layer onto Zn anode, whereas the top carbon nitride uniformizes Zn2+ flux, facilitates Zn2+ diffusion, and detaches the reactive water molecules. Theoretical simulations and structural analysis confirm the strong interactions of this SEI with Zn2+ ions that launch an ion-sieving effect to enable single Zn2+ ion conduction, and the porous and stiff feature accommodates the deposition stress and volume change under plating/stripping, ensuring consistent conformal contact on the substrate meanwhile suppressing the generation of Zn protuberant tips. Representative X-ray computed tomography study demonstrates the failure mode of the Zn anodes under aqueous electrolyte and verifies the homogeneous Zn electrodeposition behavior and spatially compact metallic structure in the presence of this hydrophobic-zincophilic SEI. Consequently, dendrite-free Zn plating/stripping at approximate to 99.2% Coulombic efficiency for 200 cycles, steady charge-discharge for 2000 h, and impressive full cell cyclability are achieved.

Automated summary

By utilizing an atomically gradient solid electrolyte interphase (SEI) strategy, this study successfully solves the irreversibility issues of metallic zinc anode in rechargeable aqueous batteries, including low Coulombic efficiency, persistent parasitic reactions, and severe dendrite growth. The results demonstrate that the new SEI structure can significantly improve the cyclic stability and charge-discharge efficiency of the battery.