Aqueous Zn batteries are promising energy-storage devices.H owever,t heir lifespan is limited by irreversible Zn anodes owingtowater decomposition and Zn dendrite growth. Here,w es eparate aqueous electrolyte from Zn anode by coating at hin MOF layer on anode and filling the pores of MOF with hydrophobic Zn(TFSI) 2-tris(2,2,2-trifluoroethyl)phosphate (TFEP) organic electrolyte that is immiscible with aqueous Zn(TFSI) 2-H 2 Obulk electrolyte.The MOF encapsulated Zn(TFSI) 2-TFEP forms aZnF 2-Zn 3 (PO 4) 2 solid electrolyte interphase (SEI) preventing Zn dendrite and water decomposition. The Zn(TFSI) 2-TFEP@MOF electrolyte protected Zn anode enables aZ n jjTi cell to achieveahigh average Coulombic efficiency of 99.1 %f or 350 cycles.T he highly reversible Zn anode brings ah igh energy density of 210 Wh kg À1 (of cathode and anode mass) and al ow capacity decayr ate of 0.0047 %p er cycle over 600 cycles in aZ njj MnO 2 full cell with al ow capacity ratio of Zn:MnO 2 at 2:1.

Aqueous Zn batteries are challenged by water decomposition and dendrite growth due to the absence of adense Zn-ion conductive solid electrolyte interphase (SEI) to inhibit the hydrogen evolution reaction (HER). Here,w e design al ow-concentration aqueous Zn(OTF) 2 -Zn(NO 3 ) 2 electrolyte to in situ form arobust inorganic ZnF 2 -Zn 5 (CO 3 ) 2 -(OH) 6 -organic bilayer SEI, where the inorganic inner layer promotes Zn-ion diffusion while the organic outer layer suppresses water penetration. We found that the insulating Zn 5 (OH) 8 (NO 3 ) 2 •2 H 2 Ol ayer is first formed on the Zn anode surface by the self-terminated chemical reaction of NO 3 À with Zn 2+ and OH À generated via HER, and then it transforms into Zn-ion conducting Zn 5 (CO 3 ) 2 (OH) 6 ,w hich in turn promotes the formation of ZnF 2 as the inner layer.T he organicdominated outer layer is formed by the reduction of OTF À . The in situ formed SEI enables ah igh Coulombic efficiency (CE) of 99.8 %f or 200 hi nT ik Zn cells,a nd ah igh energy density (168 Wh kg À1 )w ith 96.5 %r etention for 700 cycles in Zn k MnO 2 cells with alow Zn/MnO 2 capacity ratio of 2:1.

Aqueous Zn batteries promise high energy density but suffer from Zn dendritic growth and poor low‐temperature performance. Here, we overcome both challenges by using an eutectic 7.6 m ZnCl2 aqueous electrolyte with 0.05 m SnCl2 additive, which in situ forms a zincophilic/zincophobic Sn/Zn5(OH)8Cl2⋅H2O bilayer interphase and enables low temperature operation. Zincophilic Sn decreases Zn plating/stripping overpotential and promotes uniform Zn plating, while zincophobic Zn5(OH)8Cl2⋅H2O top‐layer suppresses Zn dendrite growth. The eutectic electrolyte has a high ionic conductivity of ≈0.8 mS cm−1 even at −70 °C due to the distortion of hydrogen bond network by solvated Zn2+ and Cl−. The eutectic electrolyte enables Zn∥Ti half‐cell a high Coulombic efficiency (CE) of >99.7 % for 200 cycles and Zn∥Zn cell steady charge/discharge for 500 h with a low overpotential of 8 mV at 3 mA cm−2. Practically, Zn∥VOPO4 batteries maintain >95 % capacity with a CE of >99.9 % for 200 cycles at −50 °C, and retain ≈30 % capacity at −70 °C of that at 20 °C.