Tailoring Interfacial Reactions by Lactate‐Mediated Gradient Ion Pump for Reversible Aqueous Zinc Metal Batteries

Aqueous zinc metal batteries (AZMBs) demonstrate significant promise for next‐generation energy storage, yet achieving high stability remains challenging due to the limited reversibility of the Zn anode. Herein, we introduce an affordable and multifunctional additive, lactate (LA), to form a gradient ion‐pumping solid electrolyte interphase (GIP‐SEI) that enables reversible Zn plating/stripping for high‐performance AZMBs. Through combined in/ex situ experiments and theoretical calculations, we reveal the formation mechanism of GIP‐SEI. Owing to the properties of LA anions, they play multiple roles during Zn plating/stripping: building Zn 2+ migration channel, reconstructing the Zn 2+ solvation sheath, undergoing partial desorption/dissociation, and being captured by Zn 2+ . These dynamic adjustment processes yield a robust GIP‐SEI with accelerated Zn 2+ ion migration kinetics, which significantly improves the reversibility of Zn deposition and stripping. As a result, Zn//Ti cells achieve an average coulombic efficiency of 99.6%, and Zn//Zn symmetric cells exhibit stable cycling for over 2500 h. Furthermore, full cells employing the LA‐modified electrolyte demonstrate enhanced capacity and cycling stability. This study offers fundamental insights into a functional SEI design for AZMBs and advances a new theoretical perspective for developing stable aqueous battery systems.