Water‐Lean Inner Helmholtz Plane Enabled by Tetrahydropyran for Highly Reversible Zinc Metal Anode

Abstract The reversibility and stability of zinc (Zn) metal anode are closely related to inner Helmholtz plane (IHP) chemistry. The H 2 O‐rich IHP raises severe parasitic reactions and irregular Zn deposition, impeding the practical utility of Zn anode in aqueous Zn‐ion batteries (AZIBs). In this study, tetrahydropyran (THP), a five‐carbon heterocyclic ether with permanent dipole moment and hydrophobic characteristic, is introduced as a self‐adsorptive additive to reshape the IHP. It squeezes out partial H 2 O molecules and forms a H 2 O‐lean IHP, benefitting for alleviating active H 2 O decomposition and improving the stability of Zn anode. Moreover, the adsorbed THP induces the preferential nucleation of Zn (002) plane, facilitating dendrite‐free growth and improving the reversibility of Zn anode. Consequently, the Zn||Zn symmetric cell enables to cycle over 3600 h at 5 mA cm −2 @ 1 mAh cm −2 . The Zn||Cu half‐cell can stably cycle over 400 cycles with 99.9% coulombic efficiency even under harsh test conditions (10 mA cm −2 @5 mAh cm −2 ) with 30 µm Zn foil. The Zn||NH 4 V 4 O 10 full cell maintains 92.6% capacity retention after 800 cycles at 1 A g −1 and the Zn||I 2 full cell enables to perform steadily over 10000 cycles with a capacity decay rate of merely 0.003% per cycle at 5 C.