Abstract Zn dendrite growth and parasitic reactions at the interface of zinc anode/electrolyte in aqueous zinc batteries severely hinder its lifespan in application. Herein, the zinc anode is effectively stabilized by introducing trace amounts of 4‐aminobutane‐1‐phosphate (ABPA) into the ZnSO 4 electrolyte. The ABPA adsorbs onto the surface of zinc anode and then further decomposes to a high conductive organic/inorganic composite in situ SEI layer including amino, partial carbon chain, and zinc phosphate. In the SEI layer, the residual undecomposed carbon chain promotes the desolvation of Zn 2+ , the amino induces uniform Zn 2+ plating and zinc phosphate facilitates the migration of Zn 2+ . Thus, this in situ SEI layer not only suppresses water‐related side reactions but also enhances the Zn 2+ transport kinetics. As a result, Zn||Zn symmetric cell delivers an ultralong cycle life of over 13 000 cycles at 50 mA cm −2 and 1 mAh cm −2 . A high average Coulombic efficiency of 99.72% is achieved in over 1000 cycles in Zn||Cu half‐cell. The Zn||I 2 full cell delivers a high‐capacity retention of 91.42% after 40,000 cycles. Moreover, a 49 mAh Zn||I 2 pouch cell maintains 80.28% capacity retention over 300 cycles and 61.22% after 1000 cycles.

Constructing a Multifunctional SEI Layer Enhancing Kinetics and Stabilizing Zinc Metal Anode