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Rechargeable aqueous zinc‐ion batteries are considered as promising candidates for safe and green energy storage. Yet, Zn anodes still suffer from serious challenges. Herein, an effective cation‐sieve of polyethersulfone‐modified sulfonated polyether ether ketone is developed as protective coating layer of the Zn anodes. Cation‐only transmission and dense property of the layer can protect the Zn from active water and anions, inhibiting corrosion, hydrogen evolution reaction (HER), and passivation. Zincophilic property of the layer can homogenize Zn2+ flow, and promote uniform plating of Zn. Therefore, protected symmetric Zn||Zn cell can maintain as long as 5600 h with a low polarization at 1.0 mA cm−2 and 0.5 mAh cm−2, and still long as 800 h at 5.0 mA cm−2 and 5.0 mAh cm−2. It is found that not only the dendrites but also the popular existed passivation product of Zn4SO4(OH)6·5H2O can be inhibited effectively. In asymmetric Zn||Ti cells, average Coulombic efficiency can reach 98.2%, suggesting corrosion and HER are restrained effectively. Matched with MnO2 cathode, full cells using coated Zn exhibit much better cycling performance than that using bare Zn. Moreover, Zn4O3(SO4)·7H2O (ZSH)‐assisted reversible conversion mechanism between the ZSH and ZnxHyMnO2 is revealed through operando Raman. [ABSTRACT FROM AUTHOR]

• Cost-effective and eco-friendly CEMs of SPEEK-Ms are developed. • SiO 2 -SPEEK-M possesses high cation exchange ability and low anion permeability. • ZIHC systems using the SiO 2 -SPEEK-M exhibit good electrochemical performance. Herein, a cost-effective cation exchange membrane (CEM), sulfonated polyether ether ketone membrane (SPEEK-M), is prepared through heat sulfuric acid treatment followed by evaporation induced thermal phase separation. Negative charged sulfonic acid functional groups can be grafted on the polymer chains during this process. Exchange of cations, and repulsion of anions are hence realized using this membrane. To further improve the performance of the SPEEK-M, SiO 2 is introduced in. It is found that ionic conductivity is increased to 46.79 mS·cm−1 for the SiO 2 -SPEEK-M from 19.17 mS·cm−1 for the SPEEK-M. Compared with commercial CEMs, such as DuPont N117 and Huamotech, volume expansion of the SPEEK-M is rather small after immersed in water. The membranes are then used as separators in Zn-ion hybrid capacitors (ZIHCs) with decoupled aqueous electrolytes, which includes a Zn foil anode in an alkaline electrolyte, and an activated carbon (AC) cathode in a neutral electrolyte. The electrolyte decoupling strategy maximizes the operating window of this system to 0.5 ∼ 2.2 V. The specific capacity of the AC can reach 390.0C·g−1 at a current density of 0.5 A·g−1. An energy density of 46.2 Wh·kg−1 at a power density of 3416.1 W·kg−1 can be achieved (counting the weight of AC). After gelation of the electrolytes, the growth of Zn dendrite is successfully eliminated, and capacity retention along cycling is increased to 94.3 % using the SiO 2 -SPEEK-M, which is better than that using the commercial DuPont N117 and Huamotech. The raw materials used here to prepare the CEMs are cheap and eco-friendly, which makes the membranes promising candidates as separators for decoupled electrolyte systems. [ABSTRACT FROM AUTHOR]