The aqueous gel electrodes consisting of zinc chloride, potassium iodide or potassium bromide, carbon black and polymer, such as polyvinyl alcohol (PVA), is designed for long-duration energy storage. Figure 1 shows the proposed gel electrode design. The gel electrolyte is used as symmetric electrodes for both anode and cathode, while Nafion cation exchange membrane or separator is used as the electrolyte membrane. On the anode, a zinc foil is added to provide sufficient zinc source as the zinc may be trapped in the carbon black during the repeated plating/stripping process. In the fresh prepared gel electrolyte, Zn2+ is bonded to polymer, while I- is homogeneously dispersed in the gel. During the charge process, Zn2+ is reduced to Zn metal plating on the carbon black powder, while the I- is oxidized to I2 and remains evenly dispersed in the gel system. The start electrolyte gel of 7.5 M KI and 3.75 M ZnCl2 as well as 0.2 g carbon black powder and 0.2 g PVA a[YL1] re used to demonstrated as proof of concepts, providing a theoretical energy density of 120 Wh /L. In our design, a high energy density over 100 Wh /L is achieved (Figure 2). After removing the pipe and pump system, we are able to simplify the maintenance process and promote the system reliability. Additionally, the gel system can lower the overall cost by replacing the expensive carbon felt with carbon black powder. Last but not least, the mobile carbon black powder can mitigate the zinc dendrite issue, which is frequently observed in carbon felt electrode where zinc dendrite can puncture the electrolyte membrane and cause short-circuit. Overall, our gel electrode is promising for long-duration energy storage owing to its low cost, high energy density and high reliability. Figure.2. Charge/discharge profile for ZnI2 gel battery (the volume electrolyte for positive and negative electrode is 2.3ml)